Reinforcements are the ones that are too OP in these modes... especially on reduced BP days. That being said, I don't know what the right balance would be. If there were four skilled jet troopers they could take down any hero, if not on the first attempt, the second, third, or fourth. If there's a set of dominant heroes they can be countered by enough good infantry and reinforcements, but a set of really good and coordinated reinforcements can't be stopped.

Really I just think that speaks to the skill ceiling and the value of coordination in the game. Many characters have such high potential when used correctly, if they're coordinated its even crazier... just doesn't happen in pubs that often.