Premier League tax. An accomplished guy like Valverde who has won several trophies and has Athletic Club in 5th gets the 39th position. Postecoglou who manages one of the richest sides in the world has nothing, but says 'mate' a lot.
The irony is, that precise argument was used to argue against La Liga's strength, despite dominating European competitions during that time. The criteria just keeps changing to paint the PL as the best no matter what.
Spain's domination began in 2008, months before Guardiola took on the Barça job. In fact the term 'tiki-taka' was invented because of 2008 Spain, not because of Barcelona.