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.
It is a very wise decision not to bet on a team based only on a certain period of time. You and I understand perfectly well that there are times when the team is not in the best shape. What contributes to this? Oh, there are simply a huge number of factors that need to be put together and certain conclusions made. And not everyone can do this and it takes a huge amount of time, which is always in short supply.