I don't like Neil Young's music that much either, but I would never call his songs "cheesy."
Britney/Miley/Fergie songs are "cheesy."
I just got the best of the Johnny Cash show on DVD, and there was a clip of Neil playing "The Needle and the Damage Done." It was pretty apparent that he played guitar well in 1969, so...
As far as Nirvana goes, they were hugely popular & predicted to be THE band (along with Pearl Jam) that would be remembered as having changed the music scene long before Kurt died. Yes, his death brought more fame but it's certainly not the reason for their success.