See, when I think "pioneering grunge band" I think Mudhoney or Screaming Trees or Nirvana, not Soundgarden.
I have to think of bands like Skinyard and Greenriver as being the fathers of grunge. I remember being very surprised that Nirvana was the band to break out first. I allways thought it would of been Soundgarden to break first. Man those were very bizzare days in a lot of ways especially after Never mind broke and the labels decided to sign a lot of bands around here. I have friends still paying off the IRS for taxes on the advances the labels gave out.
If I remember correctly Soundgarden didn't break sooner because they had the forethought to holdout from the labels for a reasonable deal for quite a long time.
I think 17 years of having every music critic in the world telling us Cobain was a genius far ahead of his time has clouded history a bit.
Smells like teen spirit was no doubt a huge hit, but it was released in 91 and by then Alice in Chains was already opening for the Monsters of Rock Tour...and a lot of people I knew were already big fans of Soundgarden from Louder than Love and Ultramega OK--which was nominated for a Grammy in 1989 I think.
I guess it depends on what "mainstream fans" are described as. If its people who took their love for "grunge" and moved on to bands like Collective Soul and Bush 'cause they got good slots on MTV and Curt Louder told they should like 'em...then sure Nirvana was the first "mainstream" grunge band. If you're talking about music fans that actually payed attention to stuff that wasn't on the mainstream media's rotation twenty times a day, then Nirvana was just one of a bunch of bands that got popular at or around the same time.

