There are infamous examples of overused characters in the history of the game.
Ragnarok + cStorm. Used to be, hurting anyone but Storm would trigger massive retaliation damage and generate 6 Red AP. Rags power cost only 2 and did appreciable damage while littering the board with green tiles, which meant he could spam it three times. In many tournaments, 90% of teams were these two. Outcome: both nerfed.
2Thor + 2Wolverine. They used to be a bit more powerful. Still quite a formidable team. Very common, especially in 2* teams. Both nerfed.
Spiderman. He was the best character for offense and defense. Slow to play, but most 3* teams would use him. Nerfed, then nerfed again.
OBW. If it was a 2* team, it had OBW. Nerfed.
Punisher. A fast character, I used to see him on most teams. Nothing was changed about him, he’s still a good character, but introducing Psylocke and others took his overuse.
------------------ So who is still overused?
2* Thor + 2* Storm. I see this team constantly when I see 2* teams. The playerbase-accepted solution is to buff some of the other 2*, especially Hawkeye, who was promised a buff 6 months ago.
Hulk. More health than anyone, and Anger is dangerous. He’s mostly put on teams as a “special handling required” warning when a person is finishing out a round of play. He’s an effective deterrence.
Lazy Thor. Perhaps the most dangerous defensive character, combined with lots of health.
That’s it for characters I see overwhelming numbers of. Hulk / Lazy Thor is the most common 3* team. Frequently I see Sentry, Hood, Mags, Patch, Daken, Panther, BWGS, Spiderman, Punisher. Rarely I see Psylocke, IM40, Torch, Lazy Cap. I never see Daredevil or Falcon.
And the takeaway … Magneto’s nerf should be minor. He’s not being overused right now, and the player base can’t handle another supernerf right now. 2* land seriously needs some buffs for Bagman, Moonstone, M Hawkeye, Bullseye, and now OBW. Most of these buffs should just be changes to AP costs.
EDIT: Another takeaway – Punisher was being overused, but he didn’t need any fixes at all. He’s not overused any more.