I agree with you pretty much, but my feeling is that we need to do the deliberately positive stuff first - eg. focus on fantasy works by non-male, non-Western authors and settings - before the rest of the good stuff follows. I think without a strong, definite turn away from white, middle-class, Western men too much time will elapse, in which a reaction could occur (eg. online/social media). I think the expansion/sophistication of the genre which you mention would likely happen after the positive "discrimination" (for want of a better word) is allowed to happen. Just my two pence. I wrote an Afropunk novel Muezzinland in 1998 (published in 2002) for which I received a certain amount of flak: how dare you imagine Africans, etc etc. :/
If we mean expansion in terms of which cultures we write about and how faithfully, then I think it'd be helpful, aye. Expansion in terms of the genre's range and themes and styles? I am less sold. At least short term. Most Own Voices authors are not pushing the boat out there and a great deal of expansion has been pushed prior to this point.
I would also add that in many ways, if the turn hasn't happened, it's happening. The last five World Fantasy novel awards went to two white women, one black man, two black women, and an East Asian woman - those six winner match the number of white male nominees in that period. The last five Hugo Best Novels include Jemisin's unprecedented three in a row and two white women; only four white male authors. The last five Astounding Best New Authors are one white man, one white woman, one Amerindian-Black woman, and two Eastern Asian women; I think there's maybe three other white male nominees in that time?
Looking at the Goodreads Awards for the past X years; Best Fantasy has gone to white women five years in a row in the Goodreads Choice Awards. The Can't Wait to Read/Highly Anticipated lists are more gender split, skewing male, with only one non-white person that I think I can see. The Best Fantasy Published During X Year lists - 2019, top five are all women, three have at least partially non-white backgrounds, and the highest white male is GRR Martin at 15th with a book that isn't even out there. Goodreads gonna Goodreads I guess. 2018, 4 women in top 5 (Maas got two), 2 at least partially non-white backgrounds, Mark Lawrence highest white male at 18th. 2017, two white men and three white women, with Brandon Sanderson top over all. 2016, two white men and three white women, with Michael J. Sullivan top.
These lists are not the be all and end all of critical and popular opinion, and critical and popular opinion aren't everything compared to pay disparities and difficulties getting published, or that they don't face more backlash than white males when they do wrong. But there is a very obvious swing in who's getting published and loved and I think it's happening often enough that calling them exceptions undersells it.
Incidentally, going through these lists are increases my dislike of lumping in Western whites together because in a global game, we Brits and the Americans are not on the same playing field. Maybe we have a huge influence on the whole shooting match historically but not today. Jen Williams won two British Fantasy Society Best Novels in a row and her books aren't even on the shelves over there. Not to mention how it elides the language distinction - it is far better for a writing career to be any sort of minority with an English first language that it is to be a white European without it.
