I agree, but there should still be a balance between uniqueness and uniformity. So that even when seeing the game for the first time, you can immediately understand which heroes belong to which faction. And the hero's transport is also important, just like the flag, so that you can immediately understand that it is a hero and not a unit.
This, by the way, is one of the few drawbacks of my favorite mod for the fourth Heroes game. Some heroes are assigned unit models there. And the absence of a horse and a flag is very confusing, especially considering that in the fourth game, units can move without a hero =)