My argument is that the rest of the opposition in Spain is very weak. And you don't run the risk of not getting a CL place even when you have an off season. Barca with likes of Depay would have probably struggled to get 4th in the EPL.
Having two super teams, a medium strong one in Atletico and the rest being cannon fodder basically.
Real and Barca don't run the risk of dropping out of CL places like big clubs in the EPL have done.
It's not very weak. We just went to Valladolid and Leganes last season, two relegated teams and barely forked out a win with some last ditch saves. La Liga is a very competitive league with fierce local rivalries. Despite the lower teams not having money anywhere near the level of the big teams they always give 100% against bigger clubs and the pressure is high.
We even lost to Leganes and Las Palmas at home, 18th and 19th place btw.
This goes way back. Back when Hercules beat us in our peak Barca days, we lost a league to Levante and Granada with Koeman in the end stretch of last season, and that was Messi Barcelona, and so on.
The league is very strong, just not as strong as EPL in its mid section.
Barcelona and Madrid wouldn't drop from CL places in England either. Maybe once or twice every 20 years. It's a non argument. We're talking about the biggest clubs in the world, doubt they'd fear likes of Tottenham, Villa, Arsenal and others. There's a reason Spanish sides have a clear winning record against English counterparts.
Ronaldinho Barca, Pep Barca, MSN Barca, today's Barca... all of those would have dominated EPL just like they did Spain. You can make a case that the worst of Barcelona, the one from 2021-2023, in those 1-2 seasons would have failed to make top 4. That's about it. 1-2 seasons out of 20.