He was actually playing as a 6 when he did that, Casemiro had been subbed off. You saw a young man take the game by the scruff of the neck and win it. There’s no dumb logic in wanting the nurture that further. I’m not saying I expect him to do it all the time but the capability to commit and beat men is obviously more impactful a bit higher up the pitch. I think it’s where he prefers to be too.
Ultimately where he plays depends on how you want to construct a midfield because as you said, he can play anywhere really. Personally I don’t want my 6 to be a deep lying playmaker. The burden on them is so heavy defensively, especially in England. To expect them to protect on transitions and dictate the tempo is too much I think. It’s better to have a specialist 6 who can cover a lot of ground and is quick, in the modern game one counter attack can flip the entire game.
I’ve always preferred the construction of a physical 6 breaking up play & keeping it simple, having a 8 to connect and dictate tempo and a 10 to provide the creative thrust. Of course you can have 2 sitting, a bit like Carrick and Scholes, which changes the equation a tad.