He's just not the answer to any 6 or 8 role for us, that's the main caveat, he's not good enough/doesn't apply himself enough defensively. These roles are expected to defend more and better than he currently does.
Unless I'm mistaken he's played his best football with 4 or 5 central "defenders" alongside or behind him (defense & midfield combined). Either in a back 3 or alongside combos such as Vidal/Marchisio or Carrick/Herrera. He does play some 2s with Kanté for France, but I think they play a back 3 more often than not.
Put him a winger, put him as the offensive player in a 3-man midfield, great. But he's not going to be our answer in a 2-man midfield. I just don't see it, not with our current tactic. Offensively he's a joy to watch on his day, but I think he can have significantly more of those days if we played him "better".
Could have been interesting to see him left or right (depending on what Sancho's best position is, looks to be left) with Bruno in the middle and a striker up front (CR7 now, someone else soon-ish).
Ronaldo
Sancho - Bruno - Pogba
two midfielders that can defend
This doesn't look half bad.