It is an old firm situation. Only Barca or Real can win the league. Obviously I do not mean the quality bit but no one can deny it is an old firm situation in terms of winning la liga.
Not saying la liga is isolated it is like that every major league except only la liga fans get in a hissy fit when trying to deny it
Since 1990 the following teams have won the Football League/Premier League in England:
Manchester United (11)
Arsenal (4)
Chelsea (2)
Liverpool (1)
Blackburn Rovers (1)
Leeds United (1)
Since 1990, the following teams have won the Spanish Primera Liga:
Barcelona (9)
Real Madrid (7)
Valencia (2)
Atletico Madrid (1)
Deportivo de la Coruña (1)
Since 1990, the following teams have won the Scottish league:
Rangers (13)
Celtic (7)
Comparing "recent" football history shows that a total of one whole team more has won the English league than the Spanish, and only once, while in Scotland the last time a third team won the league was in 1985. In fact, in the case of both the English and Spanish leagues, two teams (Barcelona and Madrid, and Arsenal and Manchester United) have been dominant for over a decade, and 3 teams have won the league more than once. If anything Spain at least has had two teams with roughly even success as opposed to the English Premier League, where despite fans claiming has the most competition in football, has been heavily dominated by Manchester United. While the idea that a few teams dominate is the case for every league, what damages the Scottish league is that two teams dominate to such an extent that every other league is a class apart and the third biggest club hasn't won in over 20 years. While you can go back in history and point out that England has had many more successful teams while Spain has had a couple of consistent superpowers, and this is true, but then we start getting into a different era of football and things become much more subjective.
So, to make a long story short, you are wrong.