The studio versions blow all of these recordings away
Damn right. Playing a Rhoads era Ozzy song is great fun, but recording it for a professional release? What's the point unless you are going to do something dramatically different with it.
For a one off cover, I'm usually more for sticking to the originals, but for a whole album, you really have to do something different with it.
I think the problem is that these aren't played by bands, they're done by a bunch of good musicians in more of a session musician situation, so I don't think there's as much opportunity to put their mark on it as a whole.
I like something more like the Black Sabbath Nativity in Black albums, where the bands are playing the songs in their own signature style, and they manage to add something new without needing to try too hard to be different. You don't get a lot of that when you just get a bunch of random musicians to record some tracks to put together.