I thought it was a bit obvious last night that he can't be our next best midfielder after Pogba. I think there still needs to be someone else closer to Pogba's creative ability in the midfield. City were missing Silva, and you could say Gundogan also, and still just dominated our midfield. That said, he is the closest thing we've got to a proper captain.
You're not wrong but name a single player in the world, who would have shone/played well next to Fellani, Carrick AND with tactics set up to play containment.
In a three, let's find a mobile deep lying midfielder/playmaker and let's see if Herrera can hold his own at the 8 behind Pogba. In a two, whilst he's still not perfect, he's the least of our problems i.e we need our attackers/wide players and Mourinho finding a system that can use them more effectively.
Our midfield got dominated but rarely do you see Herrera get dominated i.e he often more than holds his own. Of course that doesn't mean, he can't play bad or be bypassed but ya know there will be similar/other issues with an 'upgrade'. It's not that simple.