These are good points, JKR got a lot of heat for the "Dumbledore is gay" comment, both because it's COMPLETELY absent in the books, and, if anything, it makes his "private tutoring" of Harry where he sticks his head into a bowl of magic fluid and Harry kinda zones out for a while EXTREMELY CREEPY. I'm not really one to praise JKR for her writing, it's pretty clear she is just making shit up as she goes along with virtually no subtlety or foreshadowing, so if Dumbledore was "always gay" then she did a really bad job writing it. But then again, sexuality is invisible without deliberate and specific tells and actions, which is what makes it such an odd thing to mandate as part of "diversity".
The "Hermione is black" casting for the play is equally silly, given how the character is written and even drawn, by JKR herself, to be white. But I think the real issue with the play was just that the actress wasn't particularly attractive and folks just like jonesing for a cutie (much like the Romeo and Juliet play with Tom Holland). Though they have stuck by that casting choice for NINE actresses, across different countries, so clearly it isn't about "the best actress for the part" but a "Hermione is gonna be black forever" choice, probably because they don't want a white actress to take on the role and hear all the "ABOUT DAMNED TIME" cheers from the audience.
So in a sense I think JKR is willing to ease her "vision", such as it is, in order to keep HP feeling relevant and profitable. But she has her limits and the trans thing is one of them. I don't think she would even object to a trans character (or trans actor), though that makes even less sense in a world of transformative magic, but she WOULD object to boys with dicks showing up in the girls locker rooms (no objection to the pervy girl ghost in the boys sauna though......). HP is really de-sexed, which was appropriate up till about book 3 or so, then the notion these teens in life or death struggles wouldn't be banging left and right becomes a bit silly. Still, it's a conscious choice to remove sexuality from the books and that should extend to LGBTBBQ stuff as well IMHO.