Can I just ask how Kurt Cobain broke the mould? He didn't invent any new movement in rock, just happened to write a cacthy tune that Geffen milked for all it was worth, and still do to this day. There were tons of better vocalists working in Seattle at the time, Wood, Cornell, Staley, Vedder etc, and many of those were around the scene from it's infancy, unlike Cobain who was actually introduced to it by The Melvins. He didn't create a new movement at all, sure he was an important figure in introducing it to a mainstream audience, but I don't see how that makes him a brilliant singer.
For me the best vocalists are Robert Plant, Thom Yorke, Chris Cornell, Eddie Vedder, Layne Staley, Zach de la Rocha and Maynard Keenan from Tool.