You are right, it's not compulsory that Ruben Amorim must sign superstars or already made players before Manchester United's performance can stabilize. If Ruben Amorim can have the eye to sign players that are dedicated to playing for Manchester United, I think Manchester United can start winning their matches in the Premier League even though they don't win the Premier League title. Manchester United's problem can't be solved in one season; Ruben Amorim's target should be how to stabilize Manchester United's performance next season.
I still cannot fathom the fact that Manchester United was in their best form in the Europa League but was on their worst form in the champions league, this is not what anyone saw coming. I remembered when Manchester United signed Amorim from Sporting Lisbon, we all thought that their performance will improve and we will see them battling for the top four spot, but we never saw anything like that and their condition got worsen overtime.
Manchester United have a pretty good squad that can take them far even next season because if they were able to reach the finals of the Europa League with this squad, then they can perform wonders with this squad once again. Amorim needs to step up his performance though, because this may be his only chance to change things for this team or he may risk losing his job. He can’t go two full season without anything being achievable, he’ll soon lose his job if that happens, so he’ll need take his job more serious from next season.