Chuleta Mercury

To be fair (and as you yourself noted, but I want to acknowledge this personally as well) Drifter is word-of-god pansexual, and implied to be canonically into men. So it's still queer even if it is heteronormative, even if Eris Morn is straight. (I know this is a hot take but I'll argue a queer/straight coupling is queer. I would go a step further argue that straight couplings can be queer, e.g. a M/F heteroromantic ace couple.)

That being said, Anon, I have reading comprehension and media literacy, and understand the heart of what you're getting at. That an M/F paring in which at least one party is queer - that is, a queer M/F pairing - does not automatically subvert stereotypes. I know there's a reason so many eyes are rolled every time Disney re-debuts its "first gay couple" and it's two men having a blink-and-you'll-miss-it-kiss in the background of a shot, or a lesbian cop and her wonderful landlord wife. The presence of queer characters in a work is a good barometer of cultural acceptance, but doesn't mean the relationship is meaningful, representative, or doesn't replicate harmful ideas.

Characters are plot devices, not autonomous beings with inner lives. We cannot project onto them and claim those projections are an authentic reflection of canon. (Though I encourage defying canon where it fails and replacing it with your own, better story.) Real world queer people don't owe explanations, but the writer of a queer character needs to show, not tell. There is only what's on the page.

With all of that in mind, no, I don't think Drifteris is particularly queer-as-in-subversive. On the contrary, I think the way it's approached in canon echoes some very old and nasty heteronormative ideas about women being saved by men and men being gentled by women and a lot of this filters into the fandom surrounding it.

Why do people rally behind it then? First and most obvious is that there is an absence of good queer M/F rep so people take what crumbs they've given. I think there's strong incentive to project identity onto the media one consumes. Specifically for the claim that Eris Morn is bisexual, the cultural zeitgeist is pointed in the direction of heterosexual women being perfectly feminine, demure and helpless and so any women or female character who defies that stereotype* is automatically identified as queer, regardless of how much she likes men or how little interest she shows in women (or other genders). As well, and unsurprisingly, a number of people seriously involved in Drifteris come from the world of insipid hetero shipping and are writing to their particular tastes, and molding the characters to their tastes instead of letting the ship be informed by the characterization.

So what could be an interesting ship in capable hands comes off as tired, tropey schlock.