Heroes 6 - Discussion

Then Heroes 6 isn't "Heroes" either, because in it, heroes can move around without an army.

But a hero without an army doesn't fight. It's just an alternative to the fact that in Heroes 5, they moved around with 1 unit of tier 1. (and not only in Heroes 5)
And in Heroes 4, you could have 4 heroes in one stack and fight with them without units.