The way I saw it, it looked like him and Bagayoko pretty much both just took it in turns to rampage forwards, neither dedicated to sitting back12 goals, 9 were penalties.
Fabinho is definitely the defensive midfielder of the two. He gets forward a decent amount because Monaco either dominate possession, allowing him to come forward, or they have a very fluid counterattack where anyone and everyone goes forward in numbers on the counter - but he is the one who sits back and screens the defence.