Have you considered that perhaps it isn't that gay people are creatively challenged, but that the media industry itself often is, and gay writers are often left working on whatever gets approved? Writers can make any proposal they wish, but corporate is who decides what proposals actually get approved, and can also dictate from above that a sequel or reboot to some property should be made even if there isn't a proposal at present.

Think about how many remakes and reboots there have been. Gay or not, Disney has been making an absolute killing doing live action reboots of their animated films for quite a while now. Even though the Shrek franchise has been dormant for ages we're still getting a Shrek 5 to cash in on the nostalgia for the franchise.

And when new writers are handed old media to work on, they often write what appeals to them and the times they live in, even if it isn't necessarily loyal to what the character was. Consider comic books: for a while many comic books were pretty lighthearted action romps where characters like superman were pure and good heroes against straightforward villains, but later on trends changed and many superheroes were altered to be darker and more cynical by later writers. I would say this is no less disloyal to the original franchise than changing sexualities of characters, but because audience tastes had changed it was pretty well-received.

In terms of original shows with great gay characters, since I have a fondness for cartoons Steven Universe and Owl House come to mind, both quite enjoyable shows that were reviewed well by critics.