Perhaps a hot take, but I don't think anyone would give a shit about an "existing hero but [woman, black, etc.]" if that weren't where the writers of these films stopped. Well, okay, some people would give a shit, but we don't listen to them anyway. The real issue is that this trend has become a shorthand for lazy writing because now hack writers can just dismiss any criticism of their work, no matter how legitimate, as simply "sexist/racist whining."

Pretty much no one complains about Idris Elba being cast as Heimdall (I'm aware that some do still, but they are very clearly a minority in that opinion) because the Thor movies were (with one notable exception) actually pretty good, and even the low points in that series are still alright movies.