I think it is rather the exception than the rule that a team which is performing bad in the domestic league is one of the strongest teams in the Champions League. Yes I know that now some people will come up with examples, like Sevilla and how they won the Europa League last season when they were so bad in La Liga. But where is Sevilla now? They finished their Champions League group with 2 points out of 6 games and got destroyed in almost every game. There is a correlation between the overall performance of a team in the league and the other competitions, but yes there are exceptions of course.
Out of the UCL and couldn't make it to the Europa League spot and that's weigh bad news for Sevilla this season, they couldn't accumulate three points needed. Sevilla have suffered from the hands of inconsistent performance and their players giving nothing improving to boost their performance, other than finding good solid performance to enchanced their stats. Sevilla have failed to qualify for the next round of the UCL after falling out. They will have to fight for a spot in important positions on the La Liga table because that's the one way to stay put for another major tournaments.
Sevilla's performance this season is quite bad in all the competitions they play so I think it's quite normal for what they experienced in the UCL this season, they really don't deserve to get through the group phase and what I regret is that Sevilla didn't learn from last season when They had a pretty bad performance, but they got an advantage or luck when they managed to win the Europa League.