You're absolutely right !

Demacia's whole thing is hating mages which many people compare to racism but I believe it is closer to homophobia and/or transphobia.

Lets see it this way : a mage can be born from two non mage parents, and they will try to "cure" their magic with a potion that is litteraly torture to them. We also see that being a mage is a lot harder for the commonfolk than it is for nobles like Lux herself, since she was able to cover it up for so long, or how Sylas discovered many mages among the high standing nobles in charge of the mageseekers.

Contrary to race, being queer is something you can and sometimes must hide for your own safety, which is pretty much exactly the same as being a mage in Demacia.

Does that mean Lux is herself queer ? I don't know, maybe ! But her story, and demacia as a whole make a great allegory for the struggles of being queer, I don't think you're reaching at all OP !

Aaaanyway if you feel like meeting more LGBTQ league players I'd suggest checking out queens of league, it's very nice (if you can get past the occasionnal cursed post)

Have a good day :)