Yes, the Europa League is for clubs that cannot get the best place in the League and they will be in the Europa League, but I don't really agree if I have to say that the Europa League is not for big clubs, it's just that maybe big clubs that are used to being in the Champions League don't feel more challenged when they have to be in the Europa League compared to the Champions League. This is a fact that occurs, although many big clubs end up being thrown into the Europa League, but the ones who become champions in the end are "ordinary" clubs.
I think that's what makes UEL interesting. I mean if the big clubs that were knocked out of UCL then won UEL I think it would make UEL less interesting because it looks like a weaker competition because the champions are those who were already eliminated from UCL. But the fact is UEL is interesting to watch when "normal" teams are able to beat big teams from UCL. On the other hand UEL gives a chance for European clubs that are not in the top European clubs to play in international competition, compete with top European clubs and get attention from fans or talent scouts.