I think this thread is revealing about a lot of how we generally evaluate defencemen. With forwards, even people who don't like "analytics" use stats to back up their arguments - points, goals, etc. With defencemen (with a few exceptions) they don't, because there aren't back-of-a-hockey-card stats that measure defence. So people just use minutes played, deployment, coach's trust, and reputation to fill in those blanks.
Minutes played is not an adequate measure of how good a defenceman is, and neither is "just trust me on this, he's good", and neither is "he has a reputation for being good." People can scoff at analytics users all they want, but there really is not a way to argue productively about the relative merits of a defenceman without using them to at least some extent - otherwise it's just two sides bickering over hearsay.
Why is Provorov elite? Because Vigneault is generally considered a good coach and he plays him a lot. Now, I think Provorov has been quite good this year - not elite, but very good. A major bounceback from 18-19 for sure. I think that better goaltending and a hell of a lot of puck luck is making him (and the Flyers in generally) look better than they actually are, but I digress. By the only means we have of actually comparing defencemen's play directly, Fox had a better season than Provorov this year. Now, that may sound wrong, it might seem ridiculous that a rookie on a crummy team had a better year than the #1 defenceman on a good team, but it's true.
The argument for Provorov over Fox, aside from ice time and that he's played more seasons, is that people say that Provorov is better than Fox. For a defenceman that's usually enough - why is Doughty better than Hamilton? Because people say Doughty is better than Hamilton. Don't blame analytics users for saying "that's not enough for me."