Valour:
I mean someone with powers whose lost so much or seen their city on the brink, isn't going stop with a simple punch to the face not realistically speaking anyway. And that's what I wanna do here plus the creation of a group combating this corrupted city state, comes with all kinds of fun that we can get into along the way.
I'm not sure that's entirely true. Some people will have reservations about killing in the name of right and justice. That internal conflict is real,dramatic and interesting. Doing away with that conflict leads to the Night Lords for those of you with 40K familiarity.
That might be it's own, interesting thing although it gets away from true superheroes. Having the city corrupted all the way to the top almost turns it into Don't Rest Your Head. That's a fun idea to play with but it could get dangerously close to horror. That raises the question of what they're fighting for. If the whole thing is irredeemable, why not just leave?
How to engage the interest in fighting for the city in a game is having believable, motivated bad guys who do things that make sense and having believable, involved and interesting people and things to fight FOR. When a villain's plan gets fouled they probably won't fight to the death - they'll send some thugs to stall the heroes long enough to get away. Then they'll plot revenge, traps, work on framing the heroes or find ways to make it to painful or costly for the heroes to fight them by trying to take away the things the heroes are fighting for.
That's all system independent.