Banter aside, is there a reason they can never sell out? I know they used a UEFA protest as an excuse in recent years, but that surely isn't the reason still.
There's also statistics that say PL Champions average less total points, a smaller gap between 1-2 (aside from Spain), smaller gap between first and sixth, 4th-7th have more points, and a smaller gap between a team and the team above them.
IMO, the quality of the league isn't dependent on how many Champions League finalists a league has. It's indicative of how strong the top teams are in the league, but the competitiveness of La Liga is a joke compared to the Premier League.