Gotta say, I'm surprised at the beat down Ozzy is taking. Thought there might have been more early 70s metal appreciation.
I don't think it's a lack of appreciation for early 70's metal. Hell, many people think Black Sabbath was the first true metal band. It's debatable, of course, but they were certainly pioneers in the genre and quite unique in their time. And Ozzy was a fucking incredible front-man for Black Sabbath. No question.
I think, though, when you couch the question as "Classic Rock Vocal Showdown" people tend to focus in on the vocals alone and you have to admit, I think, that when you pit Ozzy against Dio, from a purely technical standpoint, Dio was a vastly superior vocalist.