To be honest, I am disappointed that so many people at Marvel are shown to be so thin skinned.
When Scorsese was young, he had mentors talk smack about projects he did. John Cassavetes called one of his movies a "piece of s--t" and Scorsese said that Kazan often expressed disappointment about his stuff, and his film school teacher asked him why was he bothering making movies about low-lives. Scorsese didn't throw hissy fits about it like Bob Iger did (which was really childish in his response and made him look like a fool), he took it in stride
Saying the MCU aren't cinema, that they're theme parks, or that they don't take risks and so on, is fairly mild stuff. More extreme stuff has been said by the likes of Alan Moore about the entire superhero industry and about people who work in the genre and about fans of the genre.
...to be honest, I don't really think there's a single superhero movie that is a quote-unquote "great movie" not just MCU but across the field. Some movies come close and are very good whether it's Batman Returns, or Logan, or Raimi's first Spider-Man movie or Guardians of the Galaxy but overall no.
Superheroes as a genre is quite different from anything that came before, any other genre and so on. In comics history, superheroes have swallowed and destroyed the genres of crime and horror comics that existed before, and which people have opposed to the superhero genre. So I don't know why people find it hard to accept that people who like crime movies or make crime movies or other genres would oppose superhero stuff.