No, thei're not supporters. They ARE Sjw. The staggering majority of them. And the journalists following their work too. Like a month or two ago there was this big buzz because with Bendis leaving Marvel "Finally a black writer will be writing Miles Morales' Spiderman!!!" like that is some major milestone, or makes the character and the future stories involving him better. Or remember how last year they wanted to retcon Captain America into being an Hydra/nazi sleeper agent all along, to make an heavy-handed nod to Trump's america, and were calling everyone racist neckbeard morons for not liking it?
Well okay, many writers indeed lean on the liberal side of things, which might have something to do with how being a writer is perceived as a whole - they're not the only ones though, and there are prominent libertarian/conservative comics writers who haven't been outed as complete nutjobs like Frank Miller.
But the diversity among authors is not something that should be ignored. Because even when they want to properly write about genders or ethnicities or cultures they don't belong to, it's quite likely for authors to just miss the target or falling into clichéx that range from facepalm-worthy to outright offensive. So having Miles Morales written by a black author is not meaningless. Ms Marvel achieved success because of how well-written she is, and her two authors are a muslim convert and a Pakistani-American.
I highly doubt, for example, that a white author could have created the Luke Cage series, which is shock-full of references to black culture. Black Panther would probably also have been pretty different.
I think it also works for female authors, who tend to just be better for characterization of female characters. I have read a number of fantasy novels now, and male authors tend to be pretty bad at creating three-dimensional women - which doesn't mean that their books are bad, see Scott Lynch or Patrick Rothfuss for example - while female authors like Marion Zimmer Bradley, Robin Hobb or Lois McMaster Bujold have no issue doing it. It's not always incredibly significant (like the difference between men writing Red Sonja, and Gail Simone writing Red Sonja - pretty much a rift), but I think the sample I can pick from is large enough to be significant. Which doesn't meant that female authors are better overall, mind you.
Also there's very few things in pop culture that can be as approcheable as superhero comics, and it has very little if anything to do with the race and gender of the characters. Just make good stories and good characters and the audience will come. You don't need to be a rich white guy to like IronMan, or to be a black person to think Black Panther is a cool and badass character.
I honestly consider this an issue where as a white guy I just can't have an unbiased opinion, because since I was little I have seen hundreds of heroes who just looked like me and with whom I could identify. So it's definitely not my place to say that the origins or ethnicity or gender of a character does not factor into how much you relate to it.
If you're black, or gay, or female, you are less likely to strongly relate to Oliver Queen or Tony Stark. That doesn't mean that you won't like them, just that they probably won't be the heroes you identify the most with. I've read many people saying how much having fictional characters "that looked like them" mattered - especially when they had to go through some kind of discrimination. It has the bad side consequence of some people being attached to them to the point of irrationality (like in the recent Batwoman case), but more often (and silently) than not it is simply beneficial.
Jubilee is chinese-american. And so is Daken, the son of Wolverine (if I remember correctly, his mother was chinese, and he was raised by a japanese foster family). Also I can easily name a fair few others non-mutant characters of asian origin. Radioctive Man is chinese. Mantis I think is a vietnamese american (or at least her human half, she's not a full alien in the comics). The Big Hero 6 are japanese, and yes thei're Marvel too. There's a street fighter named Shang-Chi that is literally meant to be an homage to Bruce Li in both looks and fighstyle. Coleen Wing is japanese american. And these are just a few.
I was more thinking of characters similar to Miles Morales, but Asian-American instead, like Kamala Khan. Many of those examples are villains (not exactly the characters you expect readers to create strong bonds with) or Asians who eventually arrive in America (I think Armor is another X-Men example).
