I think he was rated, because before his injury, he had a unique skill set for our team, from all of our players he is the only one who make runs behind the defenders and have the ability and pace to run on to through ball and finish. Whereas the other options Greenwood/Martial and Pogba all have either the tendency to enjoy dropping in and get on the ball, as opposed to running in behind.
This is the reason for his high goals/assists last season despite being poor for long periods, as he was always our out ball from Bruno/Pogba and sometimes even Shaw behind the opposition defense. I bet he had the most through passes received on to the space from all of our players.
However, despite all of this, he was really poor at taking players on, poor decision making on the ball, and overall he played more like a forward with erratic touches and passes with tendency to lose the ball more often than not.
It was one of the reasons why Pogba was drafted as LW, firstly it was because Ole wanted solid midfield pairing, secondly we had forwards (Rashford/Greenwood) playing as wingers and their inability to create something from the wings costed us against smaller sides. As it was mark Bruno out of the game and we would be toothless in attack as Pogba was far away in midfield and none of the others have the playmaking ability. It was also why Sancho was a priority of Ole to fill that gap.
I think a fully fit Rashford with his less erratic self coupled with play making ability of Sancho on Right hand side would make us deadly and give us something different from both sides. As we would suck teams in from right side with Sancho and then bam play behind them from left side with Rashford. It will also give him plenty of space to attack his full back one on one. So hopefully good times ahead.