Yeah I assume he will play better in Spain than in English Premier League like the others. However, Barcelona has a temporary problem with registering him. This problem will not last long if they can find a club willing to buy Christensen and one or two other players to get ride from their wages and allow to register Rashford.
Barcelona is trying their best to collect enough money to avoid being blocked with every time they try to sign a player..
Rashford himself his willing to take a cut just to be in Barcelona.. For now keeping him isn’t that much of a big problem until his load period ends and he performs to the extent of Barcelona willing to bring him officially into the club then maybe the problem could arise but I believe by then there could be some improvement for the club at large and hopefully they could let go of some players [like Lewandowski maybe as his contract also ends during that period aswell] to get fresh ones.. All will largely depends on individual contributions anyways.