Curious if you'd say you've ever seen a superhero work that genuinely deserved the alt-history genre classifier, and otherwise at what point its even possible to use it vs going 'this has decades of in-universe history but doesn't deserve to be called alt-history for [REASONS]'

Only one I can think of off-hand that has enough granulated timeline-development would be Wild Cards, but curious if you think others qualify and/or if you think WC doesn't qualify

I can't really comment on Wild Cards extensively (haven't read that much of it) but I can comment on a few other works. To briefly be the guy who talks about the same three works all the time:

Watchmen I think totally qualifies- Nixon is on his fifth term, electric cars are ubiquitous due to Dr. Manhattan's ability to synthesize lithium, Vietnam is the 51st state, the zeitgeist is consumed by pirate comics, and everyone in New York got murdered by a giant fake squid. And superheroes are real.

Unfortunately I also have to note that The Boys flirted with this; among other things, superheroic "intervention" resulted in the Brooklyn Bridge getting destroyed during 9/11, Prescott Bush and some of the other Business plot guys got wiped out during an attempted superheroic field test in World War 2, The War on Terror is being fought primarily in Pakistan, and Dakota Bob is president because George Bush Jr. killed himself playing with a chainsaw. The fact that none of this really pans out into a tangibly different society is deliberate, as part of the comic's drumbeat that superheroes, while roundly bad, also fundamentally don't matter, and are at best able to make things bad in different ways without really changing the shape of the structures that produced them.

Worm is in kind of a weird spot here- it objectively is an alternate history, countless things are different, whole nations are gone, we see a lot of alterations to the culture- but it gives limited airtime to a lot of the specifics of how things got to where they are, beyond the broad clusterfuck generated by the parahumans. To some extent, the fact that the world is radically different is downplayed until the back half because society at the start of the story is Stepford-smiling through an immanent apocalypse- and, you know, the immanent apocalypse is ultimately kind of the relevant difference from our world. But on the whole, I doubt there's a really tight worldbuilding document documenting all the ripple effects on the dramatis personae of history. The story's pretty vague about, for example, what the American presidential lineup has been since Reagan, what electoral politics look like in a world of Capes. It's vague about basically everything else in that nitty-gritty, concrete-details vein.

I do think that all of these, Worm in particular, highlight a major issue you're gonna run into when trying to do alternate universe stuff with capes, and it's that, first of all, doing really robust, thoughtful and fleshed-out alternate history is already really fucking hard, requiring a strong command of the history and culture of maybe up to the entire world, depending on the scope of your project- and superhero stuff already suffers from really strong American provincialism, so the depictions can get stupid fast if you aren't careful. Then on top of that the nature of the cape genre is that you're going to be following a pretty pared-down central cast; authorial and audience bandwidth will be tied up with what's going on with these specific guys over the course of their story, which can get in the way of a birds-eye view of their world, unless you're specifically structuring the story in a way to dodge that issue (which, you know, I get the impression Wild Cards did.)

I also think a commonality in the above works is that a lot of the alt-history changes are instrumental, included not as the result of the author trying to hyper specifically model falling dominoes from a specific point of change, but because they help the work to make its point. I doubt Alan Moore has a one-hundred-page forum thread detailing the fallout of America winning the Vietnam War, but such a thing would be beside the point- which is that God being an American Agent would fuck shit up geopolitically, regardless of the specifics. I mean a lot of this is vibes-based already, right? In objective terms the MCU has been an alternate history for years, but it doesn't claim that label, doesn't market itself as such, so it isn't. I think it comes down to whether you decide to wear that outfit on the runway, and how well it hangs on you once you've opened yourself to judgement on those grounds.