I have not read Trophy but I'm loosely familiar with it. I think you make a good point about not needing to make the difficulty increase over time since as you say, at least as-is the joint probability of succeeding at all challenges will be lower than on any individual challenge even all else being equal. I've heard many people speak really highly of the Devil's Bargain mechanic. I'll say I've read Blades in the Dark and didn't really like it, but my thoughts on it aren't so specific that I'd be above considering this.
Another possibility could be a system, I know I've read some like this before but can't think off-hand, where you have a dice pool and success is based on the number of dice that roll over a threshold (like success on 4+ on a d6) and degrees of success based on the number of successes. And then the idea of superheroes being able to give their teammates their own successes plays into the teamwork idea, but maybe it could also play into the Action Chain where you can decide how many successes to "spend" at each link on the chain, where you need to be mindful of potential surprise challenges or contextual challenges even if you have more than enough successes for every link in the chain. I'll have to give this idea some more thought but I'm actually growing to like this idea and I think it could make the overall Action Chain move a little more quickly while having an interesting meta-currency aspect to it.