Do you really need a lot of growth potential though?
No, not really.
It doesn't matter what you do with your life and health resources, is what I mean, because even extreme values aren't going to challenge game balance. If your civ was relatively normal, say the Bannor except every Fire mana you controlled gave you +5 Health and Happiness, you probably wouldn't win often against anything but Bannor without that benefit. Units are the determinators. Everything else is a modifier; units are the base value that determines how powerful you are as a civ.
If all civs behave equally well in the hands of an equally competent player than they are balanced against one another by definition.
Sorry to have implied that. I mean that "every civ can win, no question," not that "every civ behaves equally well." There is a wide spectrum of civ competence. Some civs behave far more effectively and others are moderately difficult.
I am a rather competent player of Civ and FFH, and wining on Deity in all of those is very, very hard and something I have not ever done. And whilst I am new to this mod, after playing a couple of games I can't see it happening here either
Regular Civ is challenging. RIFE is not. Maybe I'm just super-good and have no self awareness, but the AI literally can't understand almost anything you do to it. If you take, say, Alazkan the Assassin into an enemy civ solo, you can basically grind them out of existence because they'll never invent a counter-tactic. They don't understand that burning six warriors to swarm you down is preferable to what you're going to do to them if they don't do that immediately. They don't have a number of lost workers that makes them think, something has to change, right now. You can do this with almost any powerful unit, including non-hero units. Pop an Angel from a lair? Teched Assassins? Have a Mage with Air 2? That's a win against your nearest neighbor, which tends to translate into an unassailable economic and production advantage since you can usually repeat that two to three times before the game advances far enough you need to do anything different.
The AI can't counter any attack spell, assassins, recon with a fortified position, Great Commanders dropping forts, any Hero, any kind of combat healing (vampires, undead, mutation), any kind of raiding where the raiding unit will not die instantly to one of their units in range, uh, bunch of other stuff. They don't understand that there is almost never a reason to choose any religion except Runes of Kilmorph. They don't seem to settle animals. They don't know how to prioritize for the Master building they need. They can't fight back.
The only way to lose to the AI is to do the same thing that it does with less efficacy, which is to slowly stack up middling-power producible units while ignoring all the mechanics of whatever your civ is and then march them over in straight lines. Have you ever seen the Clan of Embers rush anyone effectively, ever? Calabim don't make super-vampires. The Elohim don't seek out the sites they need for their bonus traits, the ones that make every leader except Thessalonica invalid. The Grigori don't save Adventurers for Adepts and tech fire mana. They can't fight back.
Say what? Sorry but I have no idea what you are talking about. Neither of those were ever high on my list of things I need to get, and I do not see why they should be.
Then you will stand no chance in competitive PVP, no offense intended.
Let me talk about that for a second so you understand why that's usually a binary and not just "pretty good."
It is not difficult, with a Scout, good positioning, and swift teching - let alone if you go for Hunting too - to have a boar and a hippogriff by the time you're making your first Settler. Those two by themselves mean your city, wherever you stick it, is happy, profitable, productive, and self-sustaining for the first couple population levels. It's like setting next to a fully-grown Dwarven Fortress with a free Market. Those two little animals that there are tons of.
Add a bear. Add an elephant - when you can kill one you can stockpile them, they spawn at a constant level and it takes a long time before the bulls start showing up with their psychotic strength boost and aggression. With a Hunter and Subdue Animal and an aggressive exploration policy, every city you send out will be individually competitive with weaker AI capitals 30 turns after founding. Plus those Hunters can fight and kill - a Spider and an Elephant makes a Hunter better than an Axeman with Iron Weapons in open combat, and you can get more animals and buff a couple Hunters in a stack at once and then tech Assassins and oh, look, Aeron's Chosen on your seven-blooded Assassin #2...
With Runes of Kilmorph, you can spam whatever you want and build wherever you want and you'll still have thousands of gold to buy AI tech or spend on upgrades and events and whatever and your cities still have unbeatable growth potential because four Dwarven Mines is like six extra resources. Also some of them might FIND resources, they're good at that - twice as good, I think, as normal mines. Bambur is amazing because he gives all your melee 20% strength and gives all your workers a nice boost, including the Soldiers of Kilmorph you stack to build mines. Arthendain is amazing because instead of teching down the religion line, you have useful economic techs, an incredible ranged unit, and all the healing you could ever want. The Mithril Golem is amazing because GG Mithril Golem. You don't need to fight the AI for Iron. You don't need to worry about your policy techs because Arete has you covered. Earth mana makes discovering at least a few Resources near to guaranteed.
Individually these are mostly GOOD benefits, except the gold and Dwarven Mines, which are instead INCREDIBLE. But altogether, in one easy package, Runes of Kilmorph is stronger than the full contribution of many actual civs to your ability to win the game.
Some civs are so powerful or so unique that they can get along without these benefits, sort of. I mention the Scions a lot: they don't do religion (well, The Risen Emperor doesn't) and their Subdue Animal game is kinda cringeworthy with those 1-speed Recons, plus they don't need food from Boar and Elephants and Deer. But Korinna is so strong by herself she can solo many AI civs, so it's okay. You can certainly play without these benefits. But against a human who knows what they're doing, you can't just troll them to pieces with a Hero or a cutesy mechanic, you will NEED economy and long-term strength (usually, I mean, you can play Clan of Embers until you've lost a friend) and so you will need access to Subdue Animal and RoK. It's that significant. Winning without them is like winning with all archers. It's not IMPOSSIBLE, but...