Yeah, I agree with you on the time limit being lenient. I made several tiny updates after the game's submission but didn't touch that one because I felt it would change the game too fundamentally. I'll probably bump it down to 5 or even 4 minutes once the rating period is over.
You're absolutely right about the restriction! Funny story: as originally drafted, the heroes were going to be a lot more distinct, with different attack ranges, attack power levels (enemies would have had health bars), attack types (only the Witch and Priestess could hit flying enemies for instance), move speeds and health pools. Also, the Priestess would have had the ability to heal you, hence why she doesn't initially have an attack. ALL of this ended up getting because I was running out of time (and because I realized midway that enemy health bars and slower characters were bad ideas-- the Fighter's slowness ended up super annoying and I made a joke out of it).
I think the game is actually more focused and stronger for it, but it also means the characters all move as a single heroic blob. If I iterate on the concept I'll likely try to think of ways to make them more distinct again without losing the game's current simple charm.