I don't think either deserve a top 2 placement, but Nicko probably deserves a better one than Bill. The reason not many metal drummers sound like Nicko is because Double-bass got so big... but a lot of them riff in a similar manner. That doesn't change the fact that hes still way more popular than any nwobhm drummer.
And Jazzy? I think you may have him confused with Bill-Y Ward, they aren't the same person.
Bill was the first heavy metal drummer period end of story. Him and lombardo are the chuck berrys of heavy metal drumming. He should definetely be higher than Nicko.
Chuck Berry? That's your example?
I already sorta pointed out that he was the first. But again, there was no ACTUAL innovation besides being the first guy in a heavy metal band, his style of playing never really caught on outside of Doom/Stoner metal. I have no problem with Dave being at number one, he deserves it. I just think bill is more like #6. If you go by the same criteria as the performances list, Nicko wins.
Nicko's got him in skill, popularity, "direct" influence... That counts a lot more than "He's in black sabbath and was the first to do a style no one in metal really plays."