Would be an interesting change if you were going against opponents that were within your power level I suppose. Could use your C team for early matches, then B, then A team for last few fights.
But with powers and health not resetting and going against opponents that are 8 levels higher, more stars in their toons, and higher gear this is not fun or challenging at all.
Having a play mode that was challenging and interesting and you had to use strategy to complete was fun, but an impossible to complete mode without premium p2w stuff is quite annoying.
