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.
The reason why almost everyone always emphasizes that coaches should sign superstars is all because of what people expect the coaches to achieve. People believe it is through these superstar players that teams can achieve whatever they want. But sometimes, that is not the case. It's all about the dedication of the players. Someone can have average players, and it is still very possible for them to win trophies. Meanwhile, teams with the most superstars might not win any trophy at all.
So, if Ruben Amorim does not believe in superstar players, he can go ahead and sign the players he thinks can help him achieve what he wants to achieve that is the main concern. If Ruben Amorim can get dedicated players, it’s possible he could bring Manchester United back to their best form the form they’ve lost for many years and even win a trophy next season.
Even now, Manchester United has a team that, if they are dedicated, could finish in the top positions and possibly even win the league. But the truth is, it’s very bad for a team to focus on just one particular competition like what Manchester United did this season. How can a team do well in the Europa League and reach final but yet find it very difficult to perform in the Premier League and end in even top five?