I get it, about the technical ability; I can play just about anything from the first four records, and that should tell you all you need to know. But I think it's more than that. The way he put disparate pieces together (look at War Pigs; there isn't just the main riff, there are like five or six cool, independent pieces in there that all fit together nicely). Plus the material in the later Ozzy years was, in my humble opinion, very prog, and when you consider that most of that was made by two guys - Geezer and Tony - it's pretty miraculous.
We forget, too, that he was the guy in Tull for a while (well, two weeks) so at some point he was considered by his peers to be a player of some note and capability.
I'm loathe to judge players by what goes on record. There are guys - Iommi is one of them, Angus Young is another - that I just think have a bigger picture in mind. I have no doubt that they COULD play other things, but if you look at the sort of troubled history of Sabbath post Mob Rules, what was the incentive to do anything different? If anything, at that point he doubled down on the "Riffmaster General" crap (especially when Dio was in the band) and I think it hurt him. It's not what you think of when you think "SABBATH" but I think some of the stuff on Never Say Die! is really, really interesting playing.