Yeah, this. With Mou and Zlatan, he most likely thought united would be better than it is.
I think he thought he could be the star man of a team that would throw money around and be able to compete for the league and in Europe. The problem is that Man Utd haven't been anywhere near that level since Sir Alex and don't look like doing it anytime soon. Plus Pogba has shown last season/the Euros that he seems to lack the personality to lead a team and drag it forward.
Time will tell if he can become a leader and if Man Utd can turn it around. i think they probably will eventually, The problem for them is that their competitors all have lots of cash to spend.
It would be funny if they missed out on the CL again, given the money they have spent in recent years. But unless they improve significantly, Arsenal, Man City, Tottenham, Chelsea and Liverpool will remain stronger.