Which level 7 creature is the best, and why?

I still don't understand what's unclear about who's in first place. No, I don't understand how you can prove that Archons can outperform any other unit in a 1-on-1 fight when the heroes have the same stats.

Well, there was already proof of that... the situation is, of course, unrealistic, but nevertheless, the Monsters won against the Archons due to their high Attack and Defense stats.
It would seem that there's no difference: Attack and Defense should balance each other out. But no: in the case of the Monster, this rule doesn't work because it always reduces the enemy's defense by 80% and, as a result, deals so much damage that it kills even an Archon.

And in a 1-on-1 fight, with zero stats, there's nothing to argue about. The Archon wins against everyone (and even then, with skillful combat).