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.
UEL and EPL are very different and both teams have competitive rivalries and even the final result cannot be predicted. Now we should not trust any team too much. In this UEL a weak team can be very strong and surprise us one day when they reach the final round. But I also will not ignore any team because in any case Man United still looks positive because of its achievements in the past. So some people still believe in the final result that Man United will get. While some people ignore the performance of Real Sociedad which can currently destroy Man United's defense.