Varane was at his best alongside Ramos. Now I'm not saying Martinez is like Ramos in any way, but he has the same aggression and loves the dark side of the game, much like Ramos.
I think Varane needs someone beside him to bring that quality and front footed defending to get the best out of him. I think Varane is at his best reading the game and organising, which is what he has done brilliantly these past few games, along with the rest of his defensive duties.
Also, and this will probably go unnoticed for the most part, but McTominay is doing a lot of selfless work getting himself back in the box and compensating for Martinez's lack of height. It means the opposition can't target him like Brentford did, putting us on the back foot and getting the crowd going.
It's allowing Martinez to be more assured in the rest of his game, and that assuredness seems to eminate throughout the entire team.