Factions, like in Age of Empires II

Your right I'm sorry for that (still I hope someone actually understood what i tried to say xD).

btt: one faction is good enough! End of the line

I'm totally into this idea.

Best example in my mind is Rise of Nations.

I don't see why having factions with a few unique units means that each faction has to play to their unique units advantage. I admittedly haven't played much of AoE 2 so I can't say how much of an impact the faction units played in that game, but from a design standpoint I don't really see why unique units have to dominate a factions game play.

I definitely am for a large commonly shared unit selection as it greatly simplifies balancing and reduces overall costs.