It is still too early to talk about the luck factor in the Europa League this season because there are still many strong teams in the Europa League this season who may still be able to beat weak teams to become champions in the Europa League. For example, like the two teams you mentioned, Leverkusen and Liverpool will definitely dominate the European League this season to win the title with the abilities they each have at the moment.
The chances of luck at this point is very slim because not only are their many big teams in the Europa but the competition in the Europa is becoming more tensed and the desperation in the eyes of the big teams are such that they are not going to let the small teams have a chance to win rather they will make sure to utilize every of each opportunity to get to the top and probably secure the trophy, most of the weak and small teams amongst them today in the Europa are most definitely going to end their journey at some point before the semi finals and thins isn't at any point a determinant of luck rather haes work at this point until they get to the finals and it happens that they are unable to win with ease then they could say that they would be lucky at the penalty shoot out or probably by a lucky shot which could give them a winning goal.
The Europa this season is indeed going to be really tough and interesting for any team who's not in form enough and is depending on beeen lucky because you still need the form and some level of performance to be able to expect the fact that you been lucky helps you through to winning in the tournament but luck dependent teams usually have limitations to how far they can go in every of such tournament.