See, this is an objection I can understand. I'm also firmly in the camp of "if the sexuality/gender/race/whatever isn't a substantial part of the character's story, it can be whatever" - but in this case, it very much seems like it IS a substantial part of the story. If someone is an incorrigible womanizer like Tony Stark, that's not just a random fact about the person, it's a defining element of the character. Changing that is a much, much bigger deal than it would be for characters that aren't defined through such things. Same with, say, Storm being of African heritage - it actually matters for her story. Suddenly making her white or Asian would clash with that fundamentally. For other characters, this is far less relevant - which is why we can e.g. have a black Nick Fury and be entirely happy with him.
We definitely need more diversity. But we need it done in a way that's not distorting, and not ham-fisted. I'll take normalization over "LOOK AT ME I'M GAY AND HOW DO YOU LIKE THAT!" any day. That doesn't serve anyone, least of all marginalized minorities who now only get hated on even more by the already intolerant. I'm no expert in comic book lore, but it seems to me that characters for whom sexual orientation or race is some kind of crucially defining characteristic are a minority. Even among A-list characters, surely there must be room to maneuver.