The performance in the domestic league hasn't been the best indicator anyway in the past. Sevilla was so incredibly bad in La Liga the year they won the Europa League. Back then Sevilla has beaten Manchester United 2-5 in aggregate! In the semifinal they have beaten Juventus Turin and in the final they have beaten Roma. Now if you had to guess which position they finished in La Liga, you wouldn't think they finished 12th and didn't win the last four consecutive games. At some point they were fighting against relegation. That's why I have stopped predicting based on how a team is doing in the domestic league.
Usually we will use the domestic league to judge how good a team is playing, but I agree that it is not an indicator that will be completely accurate, many teams are good in the domestic league but not in European competitions, as well as there are teams that perform poorly in the domestic league but they perform well in the Europa League, as we see with Sevilla.
Actually Sevilla is not a team that is considered in La Liga, but when they are in the Europa League they are a team that is very much considered and they are even the most successful team by winning the most titles in the Europa League. They always get what they need, whether this is because of luck or not but what is clear is that they have their own way to succeed. Unfortunately now they are not in the competition this season.