On what recent evidence is he by far the best at the club? He was just as bad as any other center back last year, just given more leeway because he was a new signing plus he was injured a lot so avoided some of the catastrophic games. He is pretty clearly the worst on the ball of the main four, I don't see how you could argue that. In the air, yes he is very good, up there with Maguire, and obviously has good pace, but he has a mistake in him just like our other defenders.
I see we are eager to write him off, anyways I want to clear out something first and foremost he's a defender and that's his number one job, there's no better defender at the club than Varane, whether it's defending 1v1s or positional awareness he hold his own in this regards well.
In a team sport you need a partner to cover some of the other abilities the other defender isn't great at, as you point out he might not the best ball playing defender at the club but he isn't certainly a wrecking ball as your post suggest and he doesn't have to be as his time with Madrid Suggest, yes he had a great partner and leader with him which suggest all he had to do was be a defender, i recall his time at real he wasn't always the one to initiate attacks with long diagonal balls to teammates in space, that job was more Ramos's but Varane did help out when he had space and time.
My point is Varane would excel in this team if the defender next to him is capable of holding his own in defending and possess the Long accurate passing which Varane is not excellent at, that defender and I hope it's Martinez, would have to be the one with more responsibility to play forward passes into the Midfield and beyond.
No doubt injuries has been a norms in his time here but for you to suggest Varane isn't the best defender in our squad is the thought I won't accept.