It's fair argument EPL is more likely to produce a surprise winner than La Liga. But then EPL don't have the big guns of La Liga. It's completely logical to have more chances of a surprise winner when the top teams are not boogeyman sides. Don't tell me Liverpool who spent 30+ years without a league title is at the level or Barcelona and Madrid.
The moment Liverpool and City reached a new level, they made the league a two way fight. Problem is English teams can't hold domination. They fall off badly. Liverpool 30 years without a title, United 12 and counting. When those are the biggest clubs in the league of course you have more chances of surprising winners.
Jam is right that PL is in general more competitive, and that the Clasico sides dominate La Liga to a greater extent than Man United, Liverpool or Man City do in England (in general). But that's most because of a stronger midtable.
However, that is in large part due to the behemoths those two Spanish clubs are, as you allude to. We can debate if it is right that they're so powerful in Spain, but it's a fact that they are. La Liga had a lot of quality teams in 2010s and Barca and Real (and to a lesser extent Atletico) ruled the roost then too.
And as you have said a few times, Liverpool and Man City have dominated generally since about 2017-2018. Nobody really got close to them and City just won four in a row. Arsenal have come into the picture in the last few seasons, but I don't think it's a coincidence that their rise is coinciding roughly with City's decline from amazing all-conquering team to top team with flaws. It's not like Arsenal or Chelsea could compete when Liverpool and City were at their peak under Klopp and Guardiola, in the same way teams couldn't compete with Pep/Enrique's Barca or Ancelotti and Zidane's Real Madrid.
