Don't forget Hughes he was there too both Ozzy and DP had 3 incredible vocalists. Gillan is very controlled IMO which is why he was singing Jesus Christ Superstar for Andrew Lloyd Weber on stage. The vocalists that came out of those two bands is a who's who of sorts. It's crazy that they all had very solid side/solo projects too. Everyone knows Dio's, Coverdale's and Ozzy's but Hughes who is still doing it had some great albums as well. I love Hughes/Thrall and all the Gillan solo albums are great and very unique. The whole connection has irony everywhere. Gillan's guitarist Bernie Torme was the 1st replacement for RR after he died. He pulled it off with little time to prepare. No easy task but quit the band sighting it as a bad fit (he was a more bluesy player) One of the few to get out before being fired. There all great, it was a golden era for sure.
Yeah, its crazy stuff.
Iommi certainly had a taste for great vocalists.
Hughes could never keep his act together drinking wise to stick. His vocals on his Sabbath albums, along with the Tony Martin albums.
Great vocalists all over the place.
Cozy Powell is sort of the bridge between the Deep Purple/Rainbow thing and the Black Sabbath thing having played with all of them it seems.
Hughes is amazing however and still sounds great well into his 70's.