I am posting three links to comparisons of Rashford with other wingers from FBREF. I've compared him to Mane, Son and Greenwood. These comparisons are full of statistics - and to be honest - I don't understand all of them. These statistics are from all team matches (league and cup competitions) from this 2021-2022 season, so they include this year when critics are saying that Rashford has been shit. The stats do show that his form has been off. He has only played in 15 matches, starting 10.
While the statistics do show that he is underperforming, they also show that he is not playing as far below these other three wingers as some are imagining. Concerning his on-pitch body expressions, there is a lot of subjective interpretation. My reading is that he is down on himself and lacking confidence. Rangnick has brought in a sport psychologist; I hope that players like Rashford (and Fernandes who seems to have problems playing with Ronaldo) are willing to talk the new sports psychologist at the club.
Rashford vs Son
Rashford vs Greenwood
Rashford vs Mane