I disagree.
Dumbledore is a great and amazing character who just happens to be gay.
Just like most real gay people.
His sexuality wasn't what defined him.
There's a difference between "his sexuality isn't what defines him", and "the authour had to go out of their way to say he was gay after all was said and done, even though for all intents and purposes, his sexuality was completely irrelevant and not touched upon in the script itself".
I always just assumed Dumbledore was asexual at the point in his life Harry Potter's story takes place in because A) he had far more pressing things going on for years upon years to the point where he has no interest in sexual relations, and B) he's a sterile old man.
Point is, Dumbledore, as far as Harry Potter's actual script is concerned and how he is written is not gay, straight, or anything. His sexuality was never a concern of the narrative (unlike say,Harry himself, who was depicted as having a few love interests and acted accordingly).
So J.K Rowling coming out randomly and saying "oh yeah he's totes gay" just comes off as trying to win browny points with the LGBT community. It comes off as a literal afterthought.
Yes, you can have gay characters and not focus much on that aspect, but you should AT LEAST establish it in the script itself. Like real people, because you tend to at least know whether or not real people are gay if you know them for a good number of years (speaking from experience).
Do note that none of what I say is from a political correctness standpoint. It's from a writing quality standpoint. It's a general rule, that if you want a character to have a trait, however much of a focus of their character it's gonna be, you establish it within the narrative. J.K Rowling coming out and saying "Dumbledore is gay" is just as ridiculous as Takashi Iizuka suddenly saying "Sonic has psychic powers".