i 1000% believe that Fazio would not have solved the issue against Utd Fellani wasnt playing up against Dier but between walker and Dier and 10yrs deeper. If Fazio had gone and challenged him the gap inbehind would have been ridiculous and would have been exploited.
A lot of the balls wouldn't have gotten to Fellaini, as well as Fellaini would not have won brick in the box, including the one for second goal.
Fazio is like Lloris, you have to watch the plays he cuts out, almost more than the duels (in Lloris case, saves) he wins