I don't think Mourinho sees Pogba as being "degraded" to a central midfielder. I believe Mourinho purchased him to be exactly that in the majority of games. His strength, stamina, passing ability are all perfect for that role and with maturity will come that extra discipline without comprising his creativity.
And that's my no.1 fear regarding Mourinho's plans. Pogba lacks positional discipline as well as aggression to make that transition. He makes mistakes and has tendency for losing the ball. Citing stats: in our team Paul's got the second worst record in getting dispossessed - 1,8 per game. Add to that the worst score in having unstable touch -2,7.
He isn't a fine material for a central midfielder. What's happening is the practice of forcefully putting square pegs in round holes and his game does suffer because of it. We didn't break the world transfer record to get a decentish midfielder. Main sense behind such purchase lies in the line of thinking that the guy will be directly involved in most of our attacks using his creativity to produce goalscoring chances and that by himself he'll frequently contribute to scored goals tally.
I'd love to see your proposed central midfield consisting of Pogba, Herrera and Fabinho, because it looks to have great balance in every aspect and as of that it's got the chance to be profoundly successful.
In terms of Mata/Mkhitaryan - they aren't "wingers" but are used in the system as inside forwards. Mourinho has used these type of players in that position throughout his managerial career... From Joe Cole 04-06 to Hazard 14/15.
I'm aware of that. They can still be called wingers in such setup albeit they aren't traditional ones. Is Mata's ideal position the spot on the right wing? No, because he's ultimately a second striker. As for Mkhitaryan? Very much so, he's excelled playing from the wide position at Dortmund although it was on the right side, not the left.
The truth is though that we need a goalscorer who can come in and score 20+ a season whilst not playing as the furthest player forward. The sole reason Spurs are ahead of us this season is not because Kane has scored 21 goals - I'd expect any good centre forward playing 90 minutes every week for United to attain that. It's that Alli has scored 17 goals whilst playing deeper. The equivalent player in our system has scored 4 goals because he isn't tasked with getting into those positions.
Tottenham have a working system that suits their squad. We have 1 meaningful contributor in our team whilst they have 4 of them in Kane, Alli, Erisken, Son as well as blistering fullbacks that can cause havoc. How would Alli's game look like in comparison if he was instructed to play from deep. I guess that he would probably had lost the status of this season's revelation. It would be hard for Pogba to match the Englishman's stats, but it's not beyond realms of possibility for him to catch up with that level of importance in relation to United (he's already one of our top players). Though the only way to accomplish that is to play him as our central attacking midfielder.
It's about whole package, but if there's single area that is core to our long term success it's the one that's historically neglected for more than a decade. The midfield since the prime days of Scholes playing with Keane hasn't been great, so why shouldn't we
at last make it more than functional?! I'll underpin it:
---Fabinho -- Herrera---
---------Pogba---------