Calling the first Dio era overrated doesn't resonate with me because I don't know how it's rated.
As far as I'm concerned, Heaven and Hell and Mob Rules are the two best Sabbath albums. For my money, the first eight Sabbath albums have anywhere between 0-4 songs that I really want to listen to. By contrast, there are no skippers on either H&H or Mob.
My gateway into Sabbath was Ozzy's Speak of the Devil, which I probably bought either shortly before or shortly after Bark at the Moon was released. I didn't become a fan until after Rhoads had died so it wasn't weird to me like I'm sure it was for some others. I went back and bought Paranoid, Sabotage and Never Say Die (and maybe also Master of Reality), but the Speak of the Devil versions are still the definitive versions of all those songs. I guess my point is that, since I didn't really hold any allegiance to the original incarnation of Sabbath, I found myself comparing speak of the Devil against H&H and Mob. They compare favorably, but the rest of the original Sabbath catalog does not, so, while the best of the original Sabbath catalog compares favorably to the first Dio era, the overall original catalog does not. And, I generally like Dehumanizer, but I've never hear The Devil You Know or any of the stuff Ozzy did with Sabbath over the last what...15 years?
Also, WHY THE FUCK does the discography section at the Black Sabbath website only cover Ozzy-era stuff?