I just prefer to hold back as much as I can to make room under the mod's memory limit for projects like MCP. I have modmod ideas too, and I don't want to make them impossible because the original mod is too complex to begin with. Put in enough stuff and the mod WILL fail.
You're free to do what you want, but I'm looking for the places when I can improve efficiency. The styles that only work with one civilization and only have a handful of units seem like a waste to me. A style that can be used by three civilizations is far more appealing.
I understand what you mean. But there comes a point where you have to ask your self if you are sacrificing way too much. And I would say that this is one of those moments.
Bottom line is that if you have Germany vs Russia fighting WW2 and their tanks look the same it's just wrong. The same can be said if you are fighting Greece vs Rome vs Persia and it's all generic spearmen and archers.
Either way though, ideally once this is done (and it will take a long, long while) it would be something you can just apply as a module over top the MCP and not something that need terribly worry you. Assuming I can get it to work that way.
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This said, if you do want to look for optimizations I would suggest that instead of looking at styles just as individuals you look at them as both as individuals and as combinations.
Basically both individual civilizations and various combinations of them all have their heyday where they need to be recognizable visually. And it's these you need to hit. Outside of them you really don't have to worry that much and can merge them where it is appropriate.
For example Greece, Egypt, Rome, Persia and the other related civs need to look very different in the bronze and iron age because that is when they mattered individually and when their iconic interactions happened.
Same thing applies to the major powers during WW2, France (from the rest of Europe) during the Napoleonic wars or Japan during the era of the Samurai.
But at the same time you can easily have all European civilizations from Russia to Spain use the same model for virtually everything medieval. Your Greek heavy pikeman really does not need to look distinct from a Roman or Gallic one. What he needs to be is distinct from a Muslim one because of the Crusades.
Basically identify key roleplay eras for each individual base civ and group combos and focus on those. And than you can merge things thematically or geographically or how ever you feel is appropriate outside of it.