Actually, the Hugos STARTED going downhill, as a general measure, from the late 1990s, and the trend has accellerated to the point that it was pretty obvious 4-5 years ago.
I've voted in Hugos for 20-odd years, and while there HAVE been lovely works (Lois McMaster Bujold comes immediately to mind), the ideological slant has trended left since the I've been voting them.
I'll also note the emergence of the "Social Justice Warrior" has been a relatively recent thing, I never even HEARD the phrase until late 2012-early 2013 or so, so putting the bounds of your list 25 years before that is moving the goalposts.
The REAL issue of the Puppies, is that we believe that the STORY is the most important aspect of a work: is it engrossing, well-written, solid plot and characters. Any Social or Political message, if included, should be part of the story, not the story as a convenient vehicle to preach a particular message.
Instead, we saw more and more messages, wrapped in a story, and generally dystopic in nature. We thought that we'd like to see some nominees with good STORIES. And so Larry Correia kicked off Sad Puppies 1. And the opposition went berserk. No nominations. So Larry came back in 2014: we got no nominations. Got told that if we wanted Hugos, we had to up our game.
At this point, Larry stepped down, and Brad Torgersen stepped up. We had a list of recommendations for most of the categories. And then Vox Day/Ted Beale popped up with his alternate "Rabid Puppies" list, even bootstrapping our logo with a variant, and a full slate for ALL the categories. And we did get a larger number of people to register and nominate. So, from the numbers, did Vox and his Rabids.
The result was unexpected. A Puppy sweep of the nominations, duplicating almost precisely the Rabid Puppy Slate. And the progressive wing of fandom collectively lost their minds. In the following days, we saw widespread media stories condemning us for "stuffing the ballot box". All of which quoted progressive sources, often identically, and yet NEVER contacted anyone on our side. We were accused of standing for white male supremacy and worse, despite a broad range of nominees across ethnic, gender, and political spectrums. Our female nominees were often amused at seeing in print that they were white Mormon males.
We were repeatedly accused of being racist, sexist, homophobic, even neo-Nazis. And every time we proved otherwise, the cry of "VOX DAY!" went up. People seem to think that, somehow, if several groups of people are working towards similar ends, we MUST be coordinating action.
To which I reply: have you ever tried coordinating people who trend conservative-to-libertarian ? It makes herding CATS look easy. I don't speak for Vox. I've occasionally interacted with him over the years, and I've read his nominated works. But Vox and his "dread ilk" are independent players, and they can speak for themselves. I know Larry, Brad, and next year's trio, Kate, Sarah, and Amanda. They're good people, interested in good stories.
And none of us care bit one about the politics, ethnicity, sex, or who and how they prefer to sleep with. That's irrelevant, all we care about is a good story.
Anyway, that's my significantly-more-than-2-cents on the subject. . .