Maybe we're splitting hairs here. But it's also ok to agree to disagree on things.
I'm gonna reset a little.
I am not now, and have never been a Nirvana fan. I don't dislike them. But I don't particularly dig them, either. I say that, because I am very passionate about a handful of bands that appeared around that time (Soundgarden/TOTD, Afghan Whigs, AIC, Smashing Pumpkins, Tool, Sunny Day Real Estate, to name a few notables). I must admit it was a formidable time for me, so I am biased. I truly remember thanking the universe for Alice In Chains the first time I heard them on the radio. I was so deathly ill of the glam/hairband thing. I wanted it to die a very painful death. So that is where I'm coming from.
None of my favorite bands of that era would have had the mainstream exposure they had without Nirvana happening. I'm convinced of that. Maybe it could have been another band than Nirvana. But it couldn't have been any of the above mentioned. Even Alice in Chains. Certainly not Smashing Pumpkins. I listened to Siamese Dream this morning in the car, and am reminded of this every time I hear it. One of my all time fav albums. And it simply never would have happened, unless something more accessible before it happened. I listened to Facelift recently, and recognized some 80s-ish to it that certainly wasn't there with Dirt. What changed? Nirvana happened, for one thing.
When I say Nirvana changed everything, I mean it changed everything at that time. They didn't change the music business for good. They didn't change the rock music "world" for good. Obviously. I mean, Limp Biskit and Creed happened less than a decade later. What they did do, however, is give the pop music world a much needed kick in the behind. They were part of a larger reset. But they were also a reset button. It was reset the size of hadn't been seen in too long a time before that. And that is significant. Whether it's cyclical or not is beside the point.
I don't think Curt Cobain was a genius. I do think Chris Cornell (RIP) was a genius. I do think Cobain was very talented. In many ways he wasn't very unique. He was an honest pop music fan, as some of my favorite songwriters always tend to be. He specifically wrote poppy, hooky songs with attitude, and had tons of influences he was very vocal about. He was geeky, awkward, and somewhat troubled. He didn't try to be anything he wasn't. He was Generation X.
Now, when I say that, I don't mean he was truly the "spokesperson of our generation". I think he was in many ways emblematic, maybe not so much of what our generation actually was, but what it was supposed to be at that time. We were Generation X. We were cynical and dissolusioned by the Reagan years, and sick and tired of being patronized by bad music and sitcoms. We remembered when we could see a Talking Heads video followed by something like Asia. We remembered that the best version of Sunday Bloody Sunday could only be seen on the video from Live at Red Rocks, and not from War or Under a Blood Red Sky. We remember waiting up to see the Thriller video release. We were pissed that what had defined our generational change from the 70s to the 80s (MTV) had by the late 80s become a cesspool of spandex, stage explosions, and cheesy guitar solos.
We were ready, pining even, for the exact opposite of all that. We were ready for Nirvana, whether we really liked them or not. The fact that Nirvana were not the Beatles, Zeppelin, or even U2 was kinda the point.
I don't disagree that music industry execs were very quick to get on board with the wave. And they were certainly smart enough to know what was going to sell. Alice In Chains had some serious momentum, and arguably broke the mainstream before any "grunge" group. But they were still too.... rock.... for everyone. Nirvana was not only more accessible to the masses, but they were marketable. They were Gen-X.