Responding in this topic at this point is like beating a dead horse, but I just wanted to point out to the topic creator why Injustice won't suffer from the same widespread ignorance as Marvel players display regularly.
1. Marvel features many obscure characters from the comics and some of them haven't been featured in another medium whatsoever before the game.
Injustice's entire roster has appeared in cartoons and live-action shows over and over again. They have brand recognition. Even if you don't know anything about Deathstroke's history, you do know he's a master assassin and an ongoing antagonist to Green Arrow and the Teen Titans.
So while Marvel may be well known for their film productons, DC has done a much better job over the years of exposing the public to their characters on television.
2. Marvel doesn't explain shit about the characters or their motivations.
Injustice has a cinematic story mode that should clear up any lingering ignorance on the part of the players of who these characters are.
Your worrying about a whole lot of nothing.