Nirvana’s influence is overstated.
For one thing, grunge was a relatively short-lived trend. It got old quick.
Second, the bands that were influenced by them tended to be worse. I don’t know of any band took what Nirvana did and improved upon it. Considering that, how valuable could their influence have been?
Third, of the “big four” of grunge bands, Nirvana didn’t have the first debut album. Their album Bleach debuted in 1989. Sound garden’s Ultra-mega OK made its debut in 1988. Sound garden was also the more talented band.