Well, me neither. There's nothing great about Ozzy's vocals. He had the "luck" of being the first one of the genre, he kinda defined it so we hold his contribution in high esteem. But if we pretend he's an upcoming vocalist, I doubt many would consider him. Whenever they would pop up in history, anyone would recognize Bruce Dickinson, Ian Gillian and Rob Halford have the proper pipes. Erase Halford from Priest's history, make him an unknown guy on YouTube, and people would still go "damn, impressive" at him. Do the same with Ozzy, I'm not so sure how many would care about him.
You don't have to reach high notes and sing extremely well and flawless to be a good vocalist. If the voice fits the sound of the band, that's what matters. I don't think Ozzy is a great vocalist either. But he doesn't have to be. I prefer his voice on the 70s records over anything Bruce, Gillian or Halford ever did.
It is not a competition. It is not like you listen to a band and you say "you know this vocalist is good, but that one and that one and that one are much better, therefore... bla bla bla". I can name a thousand bands who have average vocalists, but with a voice so distinct and remarkable, a voice that really fits the sound of the band, that comparisons become futile.
Like for example... pick Andy Latimer of Camel (I know, not metal, but it's an example anyway). He's not a singer at all, but I love his voice. It fits the mood and the atmosphere of his music perfectly. The thought of "this vocalist is SO MUCH BETTER than Andy Latimer" doesn't even cross my mind.
And this goes for a lot of vocalists out there. There are many of them who sing perfectly, who can reach very low and very high notes, but very often they leave me disappointed. Either because they sing in a certain way that is irritating (vide Anneke's annoying vibratos) or because their voice doesn't fit the sound of the band well. Anneke is a very good singer. I love her voice. But I gotta say.. she has sometimes an exaggerated and annoying vibrato (specially when singing with Devin Townsend live).