1. The idea of mutations and whacky stuff is something that would really appeal to me for a funnel for a more fantasy-oriented game, but I'm not sure how well it would work for this idea. That being said, in general I like the idea that the Funnel should in some way be a monumental experience for the "survivors", so I'll think about that. In MHA, it works so well because we get the completion of the first narrative arc for Midoriya, but within the context of a TTRPG, and a first session, and a funnel where players have multiple characters and don't know who will come out of it successfully, there isn't necessarily as much of the baked-in weightiness.
2. This is a really good point that I hadn't considered, that it should be expected to be a low-roleplay, more tactical experience, given the number of characters they have to juggle and the high uncertainty of what they'll end up with. This doesn't necessarily change anything I had planned on so far, but it does change how I think about designing for a Funnel, thank you! While there definitely will be this tactical element, I think I might also borrow some of the collaborative storytelling elements of from Anyone Can Wear the Mask, if not literally, at least in spirit. Even if I don't use any mechanics from that game necessarily, it demonstrated to me how to go about playing an RPG where you aren't really roleplaying as much as doing collaborative worldbuilding and storytelling, and I think that approach could be useful for a Funnel for the reasons you state, and especially in this case since I want there to be certain superhero narrative elements that might otherwise not come through.