re: Would Kurt Cobain have been more successful than Eddie Vedder?

Define success.

If having an enormous mainstream audience is successful, then maybe.

If growing and evolving as an artist, and creating beautiful music that he loves, and that people who understand him love, and his ability to influence other artists defines his success, then maybe also.

Kurt took his art so seriously that he killed himself over it. Even though he died, he was, and still is EXTREMELY successful on both fronts, and maybe even more so than the success that Eddie's complete body of work has produced up to this point, which is saying a lot. Kurt's legacy still lives.

To be honest, it's a matter of opinion, and I love both of them.