Manchester United is aiming at winning the trophy so that they can automatically get a ticket to UCL, and to achieve this goal, United have been performing pretty good in this competition, despite the challenges that they are having in EPL. Tottenham is also in the same shoes with United but United current performance looks more promising to win the league than Tottenham, because Amorin is still building the team, and we might see a sudden change in their performance.
You are right, that's how it should be. Given their current position in the league it's unrealistic for Manchester United to qualify for a European competition through the Premier League. Their best shot at securing a Champions League spot for next season is by putting all their effort into winning the Europa League. I think Manchester United have a stronger pedigree having won the competition back in 2017 and also reaching the finals in 2022. Their experience in knockout competitions combined with a manager like Amorim who has a strong tactical approach gives them a better chance of winning the competition than Tottenham.