Not sure if this has been suggested before, but I think it would be a great idea to release some defense-oriented boosts that could be used to offset some of the extreme-damage skills in the hands of the AI.
The last few days we’ve been struggling with high-level Juggernaut, where unless you are extremely skillful / lucky at denying Red, your only chance to not be Headbutted into the ground is to “go infinite” with Modern Storm or Spidey. For example a straight “-20% damage” boost (call it S.H.I.E.L.D. support) could make the Headbutt non-lethal to more Heroes and thus give more flexibility in team composition.
You could easily do exact mirrors of the power-up boosts split by AP colour and for all AP. I think you’d need a “-xx% Ability Damage” boost or an “-xx% on all damage received”. You could even consider a small passive heal boost (please call it “Infinite Hotdogs”!) that could be used to offset the increased damage output of the high-level enemies.
Clearly balancing could take some time, and likely some (all?) would need to be rare / cost HP, but I think that this would make more design space available for balancing characters while allowing them to retain powerful unique abilities.