It is very natural when you see the favorites to win the Europa League from the status of the "big" team they have. I think everyone will do the same when 2 teams meet between a popular team and a not so popular team even though they are playing very well in the domestic league. In the end, they are the ones who decide for themselves whether favorite status can bring them victory or not.
The Frankfurt win of last year should be on minds of everyone else. We have seen some "big" clubs last year, even Barcelona was there again just like this year, and yet Frankfurt ended up winning.
This is a cup that people nicknamed "sevillas cup" for a reason, because they won it more than anyone else, even though UCL teams drop to Europa all the time. So that should tell you how being a big club doesn't matter when you are in Europa, one bad game and you would be gone, one unlucky ball bounce and you are back at home watching rest of the tournament. This is why it's quite important to remind these big clubs to put %100 into this if they want to win it.
Frankfurt has always played good football. All the players in their team play football with their responsibility to the maximum which is why their club has progressed so far. If they perform well like this, I hope they will become a good club in the future.