My feeling is sort of like this.
Diversity done right:
Hey we’ve got a character who is a vampire and also a badass vampire hunter, but let’s also make him black.
Hey we’ve got a character who is a mutant, time-traveling cop from a dystopian future, but let’s also make him black.
Diversity done…well, not wrong, but not very inspired:
Hey, Miles Morales worked and the formula worked again with Ms. Marvel so let’s go ahead and make:
Miles Morales as a female Spider-Man
Miles Morales as a female Asian-American Spider-Man
Miles Morales as a female African-American Iron Man
Miles Morales as a Latino Nova
Miles Morales as a Latino Ghost Rider
Miles Morales as a Korean-American Hulk
And so on.
Obviously that doesn’t fit every character, but that’s how it can appear. And Marvel/DC do have a history of beating winning formulas into the ground so I think fans have a reason to be a little suspicious of their motives.
And I will add that I think representation is important, particularly as Marvel has always has a diverse readership that they’ve perhaps taken for granted at times. And I am a white man so my perspective is not the same as others. Obviously if people who are not white men disagree with me and appreciate this unofficial initiative of Marvel then that’s terrific—more books for everyone to enjoy, and the more people who feel welcome at the table the better.
For me, I think there is a difference between the Blade/Bishop examples I mentioned above, and the others. It could also very well be that Big Two readers are not necessarily closed minded about women and minorities, but closed minded about character concepts that are not already firmly established. And that’s its own particular challenge.