well, many mcu characters have weaknesses too... they're just not like certain chemicals like superman. actually superman's weakness sometimes affects him... and sometimes doesn't.
also endgame made the heroes feel more human than any superhero film ever... it showed that the heroes have human emotions and weaknesses, & that a lot of times, heroes can live in denial or expect everything to work out (in the case of thor, who in ragnarok, literally said that very thing).
wdym heroes fighting spawns? :D