Put it like this, Ozzy was great in Sabbath. Geezer and Tony knew how to write to fit Ozzy's style. He hasn't worked with them since. They proved their worth with H&H, imo. I also have confidence that Rubin won't allow Ozzy to fuck up his voice with filters like he's done on every fricking album post Sabbath.
He has no stamina for live shows, but put him in a studio and give him a week or two to nail each song and I think you'll see some greatness still. Nowhere near the level of awesome that Dio pulled, but I think they could write to fit Ozzy's current capabilities and still end up with some genuinely good tracks.