Sorry if this seems like ranting, but I think this needs attention and I think many agree with me on this...
I'm watching a Marbozir LP where he's using a new mod (think it's new, I'm always the last to find out about these things; maybe it's 5 years old). This mod adds 2 additional unique slots to every civilization in the game. In other words, all civs retain their UA and 2 original unique slots (UI, UU, UB) but have two additional unique slots.
This had the potential to be a great mod for two reasons, one big reason and one small reason. The small reason is that it adds additional flavor to each civ. The big reason is that it could address the balance issue between the civs.
It appears that the big reason was one that the modder completely ignored. Marbozir randomly rolled Korea, a God-Tier civ, who along with Poland and Babylon are almost inarguable as the best civs and for almost all situations. Korea had one additional UU and a new UB. The UU was a crossbowman replacement that suffers no new penalty but has a 33% bonus against archery units and mounted units. This is an unbalanced bonus primarily because there's a few base units in the game that you need to be very limited in how much their UU get because the default unit either has a high degree of utility or a long window of opportunity. These units are composite bows, crossbows, pikes,and most importantly frigates. To give such a big bonus to a unit that already has such high utility is too much, especially when added to what's already a god-tier civ...
...and I just threw in the towel on the mod when I heard about the UB. A civ that's already as strong as Korea now getting a university replacement (similar to unit utility, some buildings need to have very limited amping up with UB, and university is the top one) a university that adds 2 culture and 2 faith. That's waaaaaaaaaay over the top.
Having trouble finding the link about what civs got what from this mod, but to do it properly civs like Korea, Poland,and Babylon would need very limited bonuses from the new additional unique slots whereas civs like Denmark, Venice, and Iroquois you could go to town with. So either 1.) rebalancing, which is much needed, was not a concern with this and the rich civs kept getting richer, or 2.) rebalancing was considered and the weaker civs got even more powerful additions, but that would be over the top. For Korea to get a university that adds 2C/2F, Denmark would need a monument that adds 10 beakers.
What Korea could have really used in this mod were two UB's that followed the mentality of the Iroquois UB. A university that adds an additional scientist slot but loses the 33% bonus, and a workshop that adds a engineer slot but loses the 10% bonus. That way, it still ties in very well with his UA, but the tradeoff keeps him in check.
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This seems to be a problem with new mods and new expansion packs. They want the mod or expansion to be something well received, and they end up going overboard with the bonuses that new civs or game elements get. When civ5 first came out, they intended for the different civs to be balanced but flavored differently, they only failed because at the time, they were unaware of some of the design deficiencies in the game - research overpowering everything else, ranged units attacking with impunity being overpowered, and growth being so critical to success. This is why with the exception of Babylon, the Aztecs, and Arabia (for the aforementioned reasons) most of the civs were relatively balanced.
But with every expansion and mod, new civs are being introduced that are better than all the pre-existing ones. There were a few exceptions like Portugal, but if you look at most of the best civs in the game they are from expansions or mods. Poland, the Maya, Korea, the Huns, Sweden, Ethiopia, Austria, the Inca, the Shoshone and Morocco are most of the best civs in the game and they are all from expansions. Then I see some of the new civs available only in mods like the Turks and the same thing happens.
We want civs that offer different flavors, not ever-increasing levels of power.
gold and +1 
production, increased to +2 
culture.
