I think the problem is that Sancho is not able to sync with the movement of Bruno and Rashford. Scholes in a interview with Gary Neville mentioned how he liked the movement of Ruud as he always knew which is the best place to receive the ball. Rashford and Bruno tend to go into areas which have tighter spaces, resulting in Sancho not being able to link up with them and having to take on more players than he would have preferred.
It is also important to understand that Sancho plays more like a attacking midfielder in the mould of Messi, where he is more precise with where he wants to pass the ball and where to receive it, rather than just dribbling for the sake of it. His style of play is only effective if his attacking team-mates are able to intelligently pick up or create spaces, which currently is not the case.