Rubin made a name for himself long before Jay Z by founding Def Jam and is more commonly associated w/ names like Run DMC, Public Enemy, Slayer, Red Hot Chili Peppers and Metallica to name only a few.
Black Sabbath and Ozzy sold an estimated 100 million records worldwide. The album could have been self-produced that it would have sold just as well given the material they came up w/.
Now, charts are just charts. What No 1 means is subject to debate. But Sabbath taking the top spot is at least as credible as anything else. Those guys have been around forever and they are THE metal band.