But is it right to have one player who have lost 11 matchs better than an other who win 3 and lose 4 ?
Personally I think it is, making the effort to play 11 matches rather than just 7 is quite significant. The point surely is to play all your matches, or at least as many as you can? Heavy penalties in the scoring for not completing matches encourages people to play more.
As a separate issue I prefer only having about 6-8 people per league because it becomes difficult tracking down all of your opponents, which is why I stepped out. But I guess the league is suffering from its own success, how many people are in it now, must be about 150! You surely have the record for largest FIBS tournaments
Considering that you have so many people interested in the league I'd say make your rules tough on playing matches so that it mainly caters to those fully devoted to playing.