Time to reconsider 12.0?
Back when the great ban of 12.0 hit there were a small number of champions that totally dominated the game and Kabam announced that the main reason they wanted to nerf them all was to make a more level playing field where players could choose to play with any champ they wanted to get through the game's content, and where there would be a larger variety of popular champions that were being used. (so they took the handful that were really good and made them suck as bad or worse than the ones that nobody liked)
Players didn't like this approach, Kabam came back and made the nerf less severe so that these champions (Scarlet Witch, StarLord, Thor, Dr Strange, Black Widow) were still much weaker but not completely unplayable. And going in to the future popular champions were never nerfed again, instead weak and unpopular champions were buffed and made stronger. (which never made anybody upset)
So now... two (?) years later and the contest is full of great champions, either newly introduced to the game or old champs that got buffed, and I would say that, arguably, there are many now that are just as strong or stronger than any of the classic champs that got nerfed. Blade, Corvus, Stark-Enhanced Spider-Man, Aegon, Domino, She-Hulk, Hyperion, Medusa, Ghost, Void, Quake, Nick Fury, etc all have some combination of utility and damage potential that make them just as strong as any of these other champs were in their prime, possibly excepting Scarlet Witch who was ridiculous.
And... those older champs never get played anymore. It's kind of sad. With Variant 2 including in its rewards 3 rank up gems that work exclusively with 2015 champions, is it maybe not time to reconsider the 12.0 nerf and possibly undo it?
1. StarLord - the nerf made the smallest difference to him; he's still functionally the same in almost every fight. He's probably fine as is.
2. Thor - since around 12.0 they also changed the way that armor works and even IF he was changed back to his original form he still wouldn't be able to do 200k damage sp3s as a 4-star, I think it's probably safe to completely undo Thor's nerf and give him back all of his armor breaking ability. She-Hulk, Aegon, Domino, Gamora, and even Winter Soldier have more damage potential at this point so why leave the thunder god gimped?
3. Dr. Strange - he was the weakest of the bunch in the first place and the nerf of Strange was really the least called-for of all of them, but he was still a really solid, versatile character that a lot of people enjoyed playing, and a reasonably good AW defender with his strong passive power gain. And now, sadly, nobody uses him. He should be changed back to how he was pre-12.0 completely. Hyperion has a stronger power gain mechanic, and Ghost Rider, Wolverine, etc. all have much stronger regen.
4. Black Widow - I think that even if you gave Black Widow back her 100% ability accuracy reduction she still would not see as much play as some other champs like Blade, Aegon, or Domino, but, I could see an argument for this still being OP. But maybe give her 100% reduction against science champs, at least? And a slight bump vs other classes. Nobody uses her anymore as is.
5. Scarlet Witch - ..... this is the one character of the bunch that I think might be better off staying nerfed. I remember people easily completing Realm of Legends with a 3* Witch back in the day. But, if you're going to leave her nerfed, at least bring her out as a 5*! She wouldn't be as dominant as she once was. And if you're going to keep her permanently as 4*-only then might as well give her back her full power. Wouldn't be able to use her in Act 6 anyway and other end-game content like Labyrinth already has built-in protections against her being so dominant.
It would be nice to see some of these classic characters dusted off in time for Avengers: Endgame and also in time for the 2015 rank-up gems in Variant 2. The meta of the game has changed.