did foo fighters already surpassed nirvana?

No because Nirvana were the kind of band that was iconic and broke new ground. Influential etc. But Foo Fighters have definately held their own.. in terms of being a successful band.

A lot of it isn't to do with talent, it's just luck and timing. The right stars need to align.. and then those sort of breakthrough bands are born. And the people in the band have no idea that it's going to happen.. and then it does.

In short, my opinion is:

Musically: Foo Fighters have surpassed Nirvana
Culturalla: Foo Fighters haven't surpassed Nirvana

They're the only two modern bands I listen to, apart from Queens of the Stone Age, but it's really like comparing apples and oranges for me, two sides of the same coin. They both came from the same musical roots. Kurt and Dave could have been today's Lennon and McCartney if he'd lived, and I'd love to see some parallel universe where Dave simply became co-leader of Nirvana.

Nothing Is Real

no, Nirvana defined a genre of music, it gave birth to something that resonates to this day. Foo Fighters are a great band but theyre not at the forefront of rock & roll like nirvana was for years. Its the same way Paul Mcartney never surpassed the Beatles though he's released his own classics.