Along with the English league, the Spanish league is the best European league, with a lot of quality teams and players.
Even for Real, it has been very difficult to win the Spanish league in recent years, but that is why they have won many more European championship titles than Spanish championship titles.
On the example of Real, it seems that it is easier to be the champion of Europe than the champion of Spain
The situation is similar with Sevilla, they are much more successful in European club competitions than in the Spanish league.
In European club competitions, it is enough to play 6-8 quality matches to win a trophy, but in the league system it is not enough and you have to play at a high level continuously.
I get your sarcasm when you say that is easier for them to win titles in Europe
But still the comparison is not quite correct. Spain has become a bit weaker as a league recently, but weaker relative to other leagues I would say. I still think it is the 2nd best as you said. But 68 quality games is first not enough, and second these quality games are much harder than league games and the consequences are a knockout in some cases. In the league you can afford to lose a couple of games, in Europe you can't.
Depending on the group the teams get, it is six games against six relatively strong teams already. Barcelona had to play two times against Bayern Munich and two times against Inter Milan, the finalist. That is four games already. Then they could have played against PSG, then Manchester City. That is already 8 games. Potentially against Real Madrid and also a final against some strong team.
Bayern Munich is the perfect counter example. They win the Bundesliga for a decade, but it is infinitely harder to win the Champions League.