To me, this stiffles creativity in team composition (i.e. people being forced into using all X-Men) and also makes balancing issues more complex. It can be done, but it would be hard to get right IMO.
I actually thought this is what the red +150% was when I first started playing and was a bit sad when I found out it wasn’t. I would love this but I do agree with ihearthawthats that, if not balanced correctly, it would result in one or two superior teams and that’s all anyone would run.
I think it is a good idea. I liked that sort of thing in X-Men Legends and Ultimate Alliance. Mix it up a little more than just Teams though as well.
Iron Man + Captain America + Thor = Avengers Triumvirate → +10% damage to Dark Avengers
Doom + Magneto (classic) + (unyet created other major villain like Loki, Red Skull, Osborn) = Master Villains → convert 1 enemy attack icon to yours
Captain America + Hawkeye + Black Widow = No Powers = -1 to all enemy AP
while it’s a good thought I like the freedom and challenge of finding a good team composition out there. I’m too much of a min/maxing at heart for these. I know I would feel drawn to just slapping together whichever ones get the synergies or feel “wasteful”