I assume that this screenhost is from the campaign (or Art of War or even Tutorial) and not from normal Gameplay.
I think it’s likely that players will only have one Hero that might just be named King (because of the very obvious crown symbol)
The fact that the other two special units don’t have a hero glow in game might mean that they are just special normal units that appear in the campaing and not real heroes.
Not sure what you mean.
You mean that there is only going to be 4 civilisations that are very different?
You can already see France and England in that screenshot having the same units types.
AoE4 is a history game. Historically the armies of England and China weren’t that different.
Chinese pole arms might look different than English ones but function nearly the same.
Not like they are literally aliens like in SC2.