Nevermind is literally the seed out of which grew all 90's butt rock
In what way aside from inspiring a bunch if copy cat vocalists to mimic his voice ckr post grunge but with everything severely watered down.
Dude can't change his voice, he did what he could with it while having interesting and provoking lyrics, good melody, and unique slund borrowing multiple genes.
His voice is probably the least important part of that tbh. Just looking at his big dumb riffs, simple pop arrangements, reliance on half-time "groovy" tempos and the loud/soft verse-to-chorus hooks, and general aesthetic, there's little difference between what he did and what the dreaded post-grunge bands were doing just a few years later.
Like, if you like them it's whatever, but you can't call Foo Fighters or one of those other late 90's bands butt rock while pretending Nirvana is somehow not.
Did you when listen to In Utero bro? ---
The above post is literally and objectively right.