It seems I have to agree with your opinion. Because we cannot deny that we determine a team's performance not far from our assessment of their performance in their respective domestic leagues. And for example, as you mentioned about Leverkusen and Liverpool who also have good performances in their respective domestic leagues.
But apart from that, in the European League, surprising results often occur. Like last season, Sevilla managed to advance to the Final even though they were in poor performance in Laliga since last season. And last season Arsenal were also in the Europa League but they lost and were unable to go further. In essence, even though we refer to the domestic league to determine which team is the favorite. But to see a real result, sometimes luck plays an important role here too.
That's true, often teams competing in the European League show different performances or vice versa, because basically they don't only target winning trophies, but tickets to the Champions League too. Sometimes competition in the domestic league is very tight, so they have difficulty finishing in the top four of the standings, so they will shift their main focus to the European League to be able to get tickets to the Champions League. Statistically, the reputation of Liverpool and Leverkusen this season is quite impressive, both have stable performance, so they deserve to be favored over other contestants.