Unfortunately, the big teams of Europe's big leagues do not think much about the Europa League. In fact, most of the Premier league teams do not care about the Europa League. Because the incomes are not as high as in the Champions League. That's why I think Barcelona's priority this year is La Liga. I don't think you can beat Real Madrid in La Liga either. Barcelona is currently in the restructuring phase. He is establishing a team that will mark the coming years and he needs time for this.
Not every team, but some teams do. I mean if you are not a team at the top 4, then you have to go to Europa. Like for example United is there right now, do you really think that United would not want to win it? Of course they would love to win it because that means some money. This isn't about preference but more about what you are forced to do.
If you can win UCL then you would love to, but if you can't because you dropped to Europa then you dropped to Europa and there is nothing else to do about it. I personally would love to just watch United win it to be fair, and that would be something every United fan would be cheering about and would be better for next year.