I feel like when you get right down to it, it's OK to have slight variations in relative "usefulness" between characters. Teamwork isn't about finding some way to objectively rate each person and then just using all the ones on the top of the list; it's about finding ways to make use of everyone's strengths and synergies the best you can, and overcoming each person's weak points. As long as a hero is fun to play for whomever's playing them, it doesn't matter if they're not quite as good as other heroes.
In addition, each hero has their own playing style, and some playstyles appeal more to some players than others. Everyone has a different idea of which heroes are the most fun. And sometimes "fun" includes playing a more difficult hero to give yourself a challenge. You really have a lot of ways to decide how much of a challenge you want in this game.
I don't believe Mister Fixer needs fixing, but it's fun to discuss alternate ways to play heroes! This has given me a couple ideas I want to try out myself.
