Just looking at other games’ mechanics can show that there is a lot of options to play with.let it be other aoe titles or completely dofferent rts titles.
I once created concepts for 7 new civs. It’s far from perfect and it is very outdated (before retold release, and I already have better ideas to implemwnt some of the concepts). But I’m just one persin so I think it’s a good prof of concept that it is possible mechanics wise to create many different civs.