One of the most overrated players ever. Had a great WC, for sure, and even then he was hardly more impressive than Umtiti (IMO they were equal in that tournament).
But for RM, sheesh. There's a laundry list of big games in both CL and Liga where he gets burned and destroyed and they concede goal after goal. Not only this season, but last season and in 15/16 too. Only in 16/17 did they actually have a good defense, usually they just won the CL otherwise with unstoppable offense/midfield and a lot of luck.
He never was the best CB in the world, unless you're really willing to say a month long period at the top during the WC (and not even that, as people overrated his performances) is a good argument for being the best.
Real God tier CB's transform a team's defensive capabilities by their presence. Umtiti's first year and a half before he started getting injured, Barca rarely conceded any goals. With VVD, Liverpool went from conceding a very high amount of goals to the fewest in the league. Godin has kept the Atletico defense among the best in the world for a half decade now, mainly because of his abilities and leadership. With Varane? RM have a shite defense and leak goals like there's no tomorrow even when he's there and he often looks bad while it happens.