I can’t think of an Avenger or even sidekick who I would put in the bottom 50% of the earth’s population. Even the dumbest are probably in the top 10-15%.
Edit: I didn’t really think of GotG as “Avengers”, but yeah, Drax and Mantis are probably gone, unless they’re somehow smart for their species. Or unless emotional intelligence is enough to save Mantis. I don’t know if we ever find out enough about Groot to know, but I’d assume he’s in the top of his species. I still think everyone else survives (Hulk survives via Banner, or at least Banner survives).