The point stands that Nirvana were an important gateway band. If you don't like the music, you should at least appreciate that some of the people that did probably grew up to make interesting music of their own or just expanded their musical horizons to the extent that the music they listen to now is a lot better than it was before they knew who Nirvana were. Look at all the bands I named in this post we can connect with Nirvana. I'll bet almost all of these bands benefited from the connection in some way. Maybe that should be the legacy of Nirvana.
Tommy, I have spent UNCOUNTABLE art lessons, car journeys, outdoor drinking sessions, house parties and goodness knows what else being forced to listen to Bleach, In Utero, Incesticide and whatever (In fact, I had to point out to two of my close friends that the album was not called Insecticide). I went through at least one year of every single one of my closest friends being
obsessed with Nirvana, Courtney-killed-Kurt conspiracies and all. Of these five guys and two girls who spent that year learning how to put on heavy eyeliner (I was already wearing lipstick) and wearing their obligatory Nirvana shirts, I can honestly say that maybe one of them actually had his musical taste improved by listening to Nirvana, and that's only because Nirvana probably got him into Placebo, which then got him into Bowie. Two of them are now cliche scene kids, and one is a pillhead. None of them, to my knowledge (And I'm still good friends with most of them, one even goes to art college with me), likes any of the bands mentioned in your post (which is interesting, at the end of the day, because I, the man who has disliked Nirvana since the first note, like at least some stuff by The Melvins and The Pixies).
It remains, that for all the rock-nerd wanking and rationalisation, the legacy of Nirvana was not turning hard rock music in to a beautiful liberal flower of loveliness and making everyone listen to your favourite eighties bands. Far from it. The legacy of Nirvana, in real world terms, was to popularise two aspects of underground music of the 80's: soft-loud singing dynamics and dischordant guitar fuzz. This set the stage for every awful mainsteam rock band till whenever it was everyone started ripping off Gang of Four and New Order again. You yourself admitted that they are entirely describable by their influences: they broke no rules, they made no advances, they merely proved commercial viability, which is always the worst measure of how good anything is.
Also, the bands you mentioned in regards to eighties rock are, to be fair, shit. Some of them I would still take over Nirvana purely sonically, but they are not what I consider when I think of eighties rock. In this case, Nirvana might be categorised, I suppose, as a positive phenomenon, in that it pushed heavy metal back underground where it belongs, in the hands of people who genuinely love it and killed off Hair Metal, which admittedly did suck, though, in my opinion, a lot less than the nu metal which rode grunges coat-tails to fame. I suppose I was more thinking of the old-school metal my friends might have been listening to had I gone to school a decade earlier. S.O.D., Slayer, Anthrax, Venom, Iron Maiden, Kreator, Judas Priest, 80's Metallica and so forth. And Motley Crue and Twisted Sister. They were good.
On that subject, I once wrote this great song and realised that I'd stolen the singing melody in the verse from, of all people, Nine Inch Nails, so I had to ditch the whole thing (I keep songs scanning properly by developing the melody in my head as I write it and sticking to that).