The thing about not looking at authorial intent is that then you erase the line between actual UST/subtext, and personal insertion of wishes, and it becomes impossible(imo) to tell which is which. This is why I don't bother with fanon: I just want the story the author is telling, not the story I or someone else wishes they were telling, and if I don't agree with the story they're telling, I either whine about it but enjoy the rest of the canon that I do like, or(much more often) I move on to something else. If I think the canon messed up, then...well...I'd really rather just enjoy something else than try to "fix" it. (Which is proof that I do not remotely have the proper fandom mindset.)

The thing about UST/subtext is if there's anything outside of that aspect to back it up. For example, Mustang/Hawkeye relies heavily on UST, but there are many other things outside of the interprettion of UST to support that interpretation, much moreso in the manga than the anime. (In the manga, the fact that Mustang's feelings for Hawkeye might be more than professional are aluded to quite a few times, and Arakawa has confirmed the shippers' interpretations/suspicions several times, including that the general who told Mustang to marry his granddaughter at the beginning of the series was Hawkeye's grabdfather. It's eventually revealed that many of Mustang's "dates" are actually is network of spies, and at least one is surprised to see him without Hawkeye at one point, and when plot reasons separate them, he talks about how, not only were his pawns and knights taken from him, but also his queen, etc.)