So news from a reliable source has come out saying Barca want to keep Rashford. So here's my two cents as someone who follows Barca very closely given all the discourse about Rashford here.
Last season Barca had a near miracle withe the only two available wingers staying fit the whole season and playing an ungodly amount of minutes especially Yamal at 17 years old. But a reliable backup was needed and given the well known financial struggles and the Nico Williams Fiasco we needed a reliable but cheap player. Most didn't want Rashford because he didn't work hard, attitude problems etc etc... so fast forward a few months and this is how things look.
Both Yamal and Raphinha have had their fair share of injuries this season and Rashford has played a lot, 1570 minutes proving 7 goals and 9 assists which is a more than decent return. Even if they weren't injured his presence has allowed Flick to keep them fresh for the latter part of the season. His play was a lot more inconsistent at first but he has slowly started to understand his role as time goes on. And most importantly he offers something different. Yamal is flair and creativity, Raphinha is goals and pressing. Rashford is neither but he offers wide threat from the byline, crossing and long shots which has helped break opposition down. The one draw back is his finishing which hasn't been as good as advertised but he has definitely been an asset.
His attitude since joining has also been great. I think he's the type of player who doesn't want to be the main guy, the pressure at United seemed like it was killing him. Here he is just another player and the media is not obsessed with him. And he seems to be enjoying that. His coach and teammates really like him and he has adapted very well. Off the field he does all the things that he did back home so yeah... for 30 mil, if he is willing to reduce his wages it's an absolute no brainer. For him aswell the move has been a great success. He's back in the England team, in a title race and one of the top scorers in the UCL. Win-Win.