Let not mixed things up here about Manchester United. They were able to finished in a reasonable position in the Europa league simply because they haven't faced any strong opponent yet. Let be realistic here, can they really be proud of their performance yesterday against FCSB? Did you see how they struggle against an unknown club? The fact that they finished amongst the top and qualified doesn't mean they are really playing good games at the moment. I'm scared they might not be able to go far in this round because they will be facing more stronger team and continue with this awful performance will eventually get them eliminated. That yesterday victory was totally not convincing at all considering how incompatible they were against the team they played against.
European League is different from the domestic league. Then, every team that plays in the European League cannot be said to be a weak team even though the European League rating is under the Champions League and it still cannot be considered that the European League is not a good league.
Manchester United appeared inconsistent in his domestic league, but faced a team that competed in the European League, Manchester United achieved the expected results.
What I want to say, every team faced by Manchester United in the European League is all the great teams in their respective domestic leagues such as Rangers and Porto.
It could be what you said about Manchester United's journey in the European League.