No doubt Real and Barcelona could compete for the title year after year. But the argument for the Prem has always been the depth compared to La Liga and Bundesliga.
But as you said, Atletico, Sevilla, and Valencia have done better in common competitions than even the best Prem teams. Conversely, when was the last time Everton or Southampton made a big run in a UEFA competition?
I’ve no reason to think Sevilla couldn’t be as successful as Tottenham and/or Arsenal in any competition.