Rashford is still a young player that is talented, he doesn't mean because he didn't perform very well like last 4 years in Manchester United he will perform poor in Barcelona, am very sure Hansi Flick what to used him next season that is why he brought him to the club. Barcelona really need champions league next season because Is the only thing they lack las season so Hansi Flick need to build new players to help him perform very well. And about Rashford and Rafinha and can says both do well last season, Rashford do is best in Aston Villa and perform very good in the club. Let see how Hansi Flick will do is next season lineup, I know if Rashford will always come from substitute or not.
I saw a video of Rashfords Training sections few days ago and I can not agree any less that he is going to do even better at Barcelona, it is a very different environment from what he had at Manchester United and the experience is going to be different to so I will go with the idea of judging him with his last Manchester United performance and think he will be doing same with Barcelona, here he will be willing to show value so that he can earn some recognition and Importance to the team so it is obviously a different mentality all together.