I don't disagree with any of that. In fact, your 2nd paragraph pretty much emphasizes the main point.
Juventus had a well functioning team, and thus Pogba was able to play in midfield without his weaknesses being highlighted, all the way to league titles as well as CL finals. Same as France, at first they were unbalanced, but then they put together a much better functioning unit and, together with the talent they had, managed to win the top prize.
Forwards are usually the star men in the team, so expecting that of Pogba is futile (even though he is very influential). However, it's safe to say that with a well functioning unit, there's no reason why Pogba can't play in midfield and be a huge net positive, and that is backed up by his body of work playing in midfield for well functioning teams. He may never get that at Utd, but that's a different matter from it being impossible.