Frankly, it's just that the Marvel ones are written terribly.
Miles is boring as fuck. Nothing ever happens. He doesn't have his own rogues, his own cast is threadbare. Almost everything he has is looted from Peter. The only real thing he has to his name is one of his powers... but Venom Blast is a narratively fucking awful power. The threat of a situation is massively diminished when it's been established that Venom Blast pretty much takes down anyone.
Riri and Moon Girl are insufferable. Riri's comic is essentially mental masturbation as everyone talks about how great she is. Moon Girl is boring in her own series and treated as a walking McGuffin in others.
Cho has just about been character assassinated in half the books he appears in. If they're going to fuck with his personality, the least they could do is go into greater depth about how the Hulk is effecting him.
I got no problems with "Black Spider-man". I have problems with Miles Morales. Kamala Khan and Kong Kenan (maybe it's the K names) are both fine characters. They have their ups and downs but at the very least they're respectful to their source and actually have solid character development.
If Marvel wants people to stop complaining about new, diverse characters they need to make new, diverse characters worth reading.