OP's problem is that King is easy and so beating the ai with a generic no bonus civ would be possible, meaning that he does not appreciate the bonuses some civs have later in the game because on king you are already so far ahead that it doesn't matter, but on harder difficulties you are still fighting for victory. He also seems to play exactly the same way regardless of the civ and not try to use their abilities well.
So bump the difficulty up if the game is too easy.
As title?
America : I almost never buy tiles and i dont see how this is useful unless you are going liberty and trying to get AIs to DOW you for buying tiles near them...no early game units/buildings also hurt in the critical part of the game
Lots of people buy tiles. You say that having an early advantage is great, buy the best tiles in range and work them. Great for tall play as well because your cities need to be working the best tiles they can. +1 sight is also amazing for scouting and getting ruins.
Assyria : You want to be in the tech lead, not behind it...and the UA only works by incurring tons of warmonger hate. +10 xp fro a library is ok i guess, but its not enough to bump you to the next experience level.
Tech the bottom half or the tree and use the military bonus you get to then go take the top half of the tree from your neighbours. The +10xp from the great work is like a mobile barracks that you can move from one city to the next. In difficulty levels above easy, you will be behind on tech during the era when you get the siege tower so you can make good use of the UA and UU.
Austria : I rarely want to puppet/annex a CS vs giving them 1k gold and enjoying the unique bonuses. CS placement is also often not that good. I dont see the point of +25% GP gain from the coffee house, wouldnt you normally have your GPs spawning in your capital where all your bonuses are concentrated anyway?
Most people work the science specialists in each city meaning that they spawn GPs from every city. +25% bonus across every civs is amazing. Only working specialists in the capitol is suboptimal, and is an important part of tall play.
Bablyon : Archer bonus strength doesnt stay with upgrades and walls only work if your cities get attacked.
The UA needed to balanced by having weaker UU & UB, but instead they got a super archer as well.
Brazil : Not impressed by tourism bonus, would have preferred a culture bonus instead.
Playing on King i can win tourism with no concert tours before the Atmoic era. On harder difficulties you cant and the tourism bonus is then amazing. They do also get a culture bonus from the UI anyway...
Byzantium : Bonus vs naval ships is rather useless given that the AI shys away from naval forces (aside from keeping outdated tiremes around for some reason)
Your first ship is a ranged ship. Ranged >>> Melee. This ship is amazing for killing other navies and can help out by shooting land targets.
Carthage : Free harbour isnt very impressive, most of your trade will be going from your capital anyway, so you only really need one harbour (till you research seaports). And ive never had a game where i really needed to cross mountains...
Free city connections without waiting. Bonus gold that grows bigger as the game goes on. For me the main point of harbours is not the trade routes but the city connection gold. Crossing mountains can be great for pushing past choke points, and can be hilarious in mp because people forget about it and then get stomped as an army flood over the mountains into an unguarded area completely bypassing their defences. Or just send a few cav unit to pillage every tile they have.
China : +2 gold from paper makers is a drop in the bucket compared to the much more useful +2 happiness other unique buildings get.
Its +3 gold effectively due to also getting rid of the maintenance cost, early game warmongers struggle with gpt, this really helps to offset that. But yes happiness is better than gold, but china has the chu-ko-nu and super generals so having a super happiness UB would make them OP warmongers.
Denmark : Viking fury isnt very useful unless you on a water map, same goes for vikings and norwegain ski infantry is too terrain dependant (you dont even want to have cities in tundra/snow if you can avoid it)
Denmark are pretty weak. Every water civ is weakened by being on land maps. The infantry does also get its bonus in hills, which are all over the map, not just snow and tundra.
Egypt : War chariot is too terrain dependant, and not needing horses is hardly a big deal.
Not requiring horses means you can more than 2-4 of them, generally their is some open plains civ that you can crush with them, killing a rival and grabbing some puppets and a good city in the form of their cap. The burial tomb then helps to offset the unhappiness from the warmongering.
France : Double the theming bonus only kicks in much later in the end game, requires you to win wonder races and isnt a big bonus in the first place (like 2 or 3? And you need to wait for the AI to swap the correct ones with you, which is hard as you cant request specific eras/etc). The pre-BNW culture bonus was much more useful IMHO. Chataeus are also too location dependant.
the theming bonus is not great (and is worse that Ancien Regime) but it is possible to get up to about +12 normally from theming from a few wonders (and national ones also having theming bonuses). You can request the Great Work that you want to trade for... Chataeus can be built next to luxuries of which you should have quite a few around each city, so I dont see what the problem could be.
Germany : Having barbarian units join you isnt that useful when an archer or two is enough to handle everything except raging barbarians. Also if you have raging barbarians on, you would be better off keeping an encampment alive to farm honor, rather than destroying it.
Saved production from building units. Or just bonus gold if you dont need them any more and delete them. Can rush an opponent while building infrastructure in your cities.
Greece : I dont find influence degradation a problem at all? Especially if you are in the lead, you automatically get tons of influence for being top cultural, faith, etc gains.
City states are easy to keep on easy difficulties. On harder one the AI actually can challenge on the faith/culture/tech missions and are much more active about clearing encampments.
Indonesia : So from what i can tell you get two copies of a unique resource per new continent city you found. I found this pretty hard to get as by the time you research astronomy, the other continent is fully settled as ti is...unless you play on an island map. On continent plus, i found myself forced to settle island cities in very poor locations (mostly water tiles, no production) to get the bonus. Kris swordsman bonus seems random and im not sure what it does...i got "evil spirits" but could not see the bonus in the pre-battle popup. Im not sure if the promotion stays when you upgrade the unit either.
Yeah, only good on island maps otherwise the UA is too hard to use. The Kris get a random promotion after their first battle, mouse over it to see what it is. I do belive the promotion stays on upgrade.
Korea : I dont see why you would use turtle ships when frigates are superior, also turtle ships instead of caravels means you cant use caravels to explore and become the first world congress host.
AIs can and will beat you to having both Printing Press and Astronomy on higher difficulties so not founding isn't much of an issue. Korea's UA is amazing enough to make up for lacklustre UUs though.
Mongolia : CS are easy enough to attack as it is, this ability just seems pointless.
Keshiks OP. Khans just make that even more so. They dont need another boost
Morroco : I find that its often far more profitable to have multiple trade routes to one large civ than multiple smaller ones...and the bonus is so minor that it doesnt help, especially in later games. Also the kasbah is pretty lackluster as it doesnt scale with techs that improve yields.
Kasbah turns worthless tiles into useful tiles. Combine with petra and you're golden. Generally each capitol is worth more than a civ's second cities, so sending a route to each capitol is generally the best and this further enhances it. (the UA bonuses dont come up as part of the trade route screen). It does die off later in the game though, but as you keep saying, early snowballing is more important that late game effects.
Persia : You cant really control when golden ages happen, so the military bonus during golden ages can get wasted. If you could save golden ages though, this becomes top tier.
You can time both when golden ages happen, and when you make a military push. Easy enough to mix the two together.
Polynesia : Maoi is probably the worst improvement in the game.
Maoi is very situational, but sometime can be good. Useful to build a line in the thrid and fourth rings of a city so you dont get many worthless ones in working range.
Rome : Unit bonus strength doesnt stay with upgrades and the +25% production bonus is pretty pitiful (especially with puppets) in practice. Now if it was a production bonus in the capital...
Buy the building in the cap. Then every city gets +25% production bonus. Who cares about the puppets anyway? +25% production for your (annexed) cities is amazing
Russia : +1 production for strategic resources isnt much considering how rare they tend to be. Double quantity isnt useful at all until you get to coal and later, its quite common to end up with way more iron/horse than you can possibly use. Krepost doesnt seem to do much either.
Early hammers. Snowballing. I often find myself limited by the amount of strategics available on standard, doubling that helps.
Songhai : Amphibious/War canoe are not very impressive unless you are on a water map, a better bonus would have been no extra movement cost for crossing rivers...
The bonus also applies for attacking over rivers, which people often use as their defensive line in mp.
Spain : Im not even sure if they have a start bias for natural wonders, but given that theres only a max of 4 wonders on a standard map with 8 players, your chances of getting the 500 gold is very low. Conquistadors also come way too late in the game, by the time you get it, the other continent would be fully settled anyway...
No NW bias. Just build a scout or two and find them. Conquistadors are lacklustre, good for wide play on island maps though
Sweden : 90 influence is frankly not much, and influence ceases to be an issue later in the game. +10% to GP generation is also pretty low. Hakkapelittas are a melee combat unit that stacks with great generals, but Sweden has no bonus to GG generation to make full use of it and having a GG stacked in the same tile on the front line just screams "kill me!". To top it off, +15% bonus from having a GG stacked is not even very high.
+10% per friendship. Make 5 friends and you have the same bonus as Babylon but also extending to your GWAM (the same as a GA Brazil). Gift excess Generals and Admirals. The stacking also doubles the Great General bonus!
Celts : Unimproved forest, lame. Pictish warrior is also pretty weak in my experience, especially after swordsmen come out.
1st Pantheon. 1st Religion
Iroquious : Weaker jaguar warrior (if you upgrade jaguars to swordsmen, they are far better) and the longhouse is actually weaker than a normal workshop for some reason...
Pretty bad
Maya : Atlatist gets obsolete too quickly.
Lasts longer than archers due to earlier availability and allows you to focus on other techs without having to pick up archery till later.
Netherlands : Much weaker version of the Arabia UA and a unique improvement that only works in one of the worst terrain types in the game (marsh) and is only equal to a farm + bonus yield from tech (taking into account the marsh food penalty). Sea beggars are not impressive considering that naval engangemetns (and coastal attacks) are decided by mass frigates rather than suciding melee ships into coastal cities.
UA < Arabian UB.
Try some city attacks with UU melee ships, they can be quite effective at it, but still aren't better than frigates, but they are resourceless.
Polders turn the worst terrain into the best. clearly you have never built them.
Ottomans : Oh look you just captured some outdated tiremes, really useful there. Or you could just mass frigates like usual.
Capture the triremes with your triremes then just hammer a coastal city with. Suicide attacks. Or steal SoTL and battleships with them later on.