Yes it may be that the Europa League is interesting and Manchester United always performs well in this league. But Manchester united couldn't play well in the Premier League. Since Manchester United cannot perform well in that league, they may now be focused only on the UEFA Europa League. Maybe they can succeed in this. I would like to compare some of their performance, that is, comparing their Premier League performance and the performance of the UEFA Europa League.
According to me Manchester United have defeated twelve matches in the Premier League but they have not been defeated in any match in Europa League. So their performance in the Europa League is definitely getting better.
The comparison you made is not enough to say that United performance has improved in this UEL competition, first this competition is very different from the English league, it is very clear that the English league is much more competitive than the UEL, second in the league phase United have never met a strong team so they do not feel defeated. In this knockout round they will meet a strong team for the first time if you look at the match between Real Sociedad and Real Madrid yesterday it can be concluded that it will be very difficult for United to beat Real Sociedad. I am quite doubtful that Man Utd can continue their journey in this competition.