Foreign teams put more effort into the europa league and rightly so, the issue with this country is the obsession with the champions league which actually means teams don't put out their best players for the europa league or have their eye elsewhere. When was the last time a team apart from barca or madrid won the la liga? 2003-04, so it goes to reason that the clubs in spain will do better in the europa league. Also the last time a team aside from barca or real won back to back titles was 1983-85 (nearly 30 years) which was Athletic de Bilbao. Overall the premier league is a stronger league but the la liga is more technical.
Other countries also help their teams in Europe, by manipulating fixtures. We seem to do almost the exact opposite, at times. I hate to stick up for City, but their CL campaign was hampered by the dubious nature of their fixtures. They were away from home in the league after every single group game (6/6). With their focus on winning the Premier League, it took a toll on their European form.
As I alluded to earlier, watch Malaga. They are backed by oil money, have already bought their way into the CL, and will most probably be challenging for th title soon.
"We must go by the rules" "Who made the rules?" "We did" Basically if there was enough will to change the rules they would be changed. If Barca or Real finished 4th and suddenly got excluded from the CL (OK very unlikely but you see my point), the rules would probably change 'more rapidly'. Always amused by authorities that say rules cannot be changed when it's their own rules.