Barcelona and Madrid do have an "easier" league to play in in relative terms.
One sensible way to look at it is the table for half-time leads. The big two in Spain do crack over 50% for this statistic, Madrid are up at 68%, Atletico 44%.
http://www.soccerstats.com/table.asp?league=spain&tid=h
Comparable tables for England and Germany:
http://www.soccerstats.com/table.asp?league=england&tid=h
http://www.soccerstats.com/table.asp?league=germany&tid=h
There's a very clear difference in this statistic as you go from Spain down to Germany down to England, where Leicester has the highest percentage at 38% and the rest of the successful clubs are sitting at around a third of matches.
Leading at half time means coming out for the second half to convert a goal advantage into points. It means controlling tempo and effort, and it means a high chance of being able to use substitutes to manage player fitness and avoid recurrences of injury and suspensions.
As we all know our squad tends to get leggy during the most congested periods of the season, like the one we're in now. We struggle to deal with it because we need our best players on the pitch playing with maximum intensity in nearly every match.
Meanwhile, the outstanding factor in Spanish football is the skewed distribution of TV revenue to the big two. You don't have to denigrate La Liga in general to point out that the quality gap to Madrid and Barcelona is huge. Atletico's progress in recent years is surely better interpreted as an outlier of canny management and great morale than as an indicator of the great depth of the league.
This is why I think Guardiola will end up being just another manager at Manchester City. Pellegrini was able to coach Madrid to nearly 100 points but he sure as shit can't manage that at City.
