If it was true, then, why did Arsenal, Manchester United, and Liverpool always fail to win the Europa League last seasons? I think it's not completely true to call winning the Europa League easier than getting into the top 5 of EPL. It seems to me you're underestimating the teams in the Europa league.
I believe the Europa League is being counted as a major trophy. It's less popular than the Champions League. It offers a small reward. If it had a big prize like the UCL, top clubs would want to play in it.
It's clear that nobody has a guarantee to win anything. While people can say that the competition is weak, we all know that when it comes to knockout stages, we are going to end up with some trouble, and because of this we are going to have some trouble with it as well. I believe that we need to make sure that things aren't always that complicated, and because of this we need to arrange something that will take a while, and this means that we need to see United do better before we can make these claims.
And even after that, even after they play some games and look like they are doing better, then we will not still know for sure if they are going to win or not. So far they have been terrible, which means that they are going to have even harder time, and that is why I believe that we can't really safely assume how they are going to do.
Just because they changed their coach, and probably got a much better one, doesn't mean that they are good enough to win Europa now. That just means they will be better than how they have been so far, and that may still not be enough. We just have to wait and see, you can bet on them to win if you want, I will not do that before I see how Amorim will do.