He was still one of the forerunners, whether you want to argue if he's "good" or not. He was around before Eddie Vedder and all those other guys came into the forefront -- and though behind the scenes I'm going to be all for Vedder because that's how I roll, that doesn't undermine Cornell's participation in the creation and perpetuation of Grunge.
The way I see the Timbaland thing: An artist has complete license to dabble in as many genres and styles as he wants to... just don't expect us to jump on the bandwagon.