Good points. I was cutting and pasting them up for a rebuttal, but I'm not sure I really disagree with you, especially about Nirvana not being the death knell for all things metal and macho. Nirvana is just shorthand for a major cultural shift happening, something that would probably take a ton of screen space. Instead of describing that shift, it becomes easier to just write "Nirvana," which is lazy and sloppy, but is how I approached it in comment. That's on me, and doesn't quite do what happened justice in its accuracy.
But, one quibble. I mean, maybe I pay too much attention to that which is led by critics, but acts like Kid Rock and Limp Bizkit? They were discredited even while they were big by opinion and taste makers. The question, I guess, is how serious do we take opinion and taste makers, or do we enter into evidence the success of the bands, which I would say was due to the record labels' last gasp at supply-dominated airwaves and distribution rather than any popular demand. Once Napster hit, those bands? Dead.
That said, you certainly have a point about the death of genres being because of lesser bands taking up the mantle.
And those acts were big, for sure. So where that leaves me, I'm not sure. Clinging tenuously to an idea that the moment was precious and doomed, I guess.

Maybe?