Tosic and Diouf straight up dominated in Germany, what planet exactly are you living on? Tosic was there, what, three years ago? He had a good 6 month loan at a relegation candidate club! He is hardly a relevant talking point. Diouf is doing well over there but he is not 'dominating' the league, is Michu, formerly a lower level Spanish player, 'dominating' the Premier League?
There are so many variables that could of affected Sahin's failure in Spain and England, or, for that matter, any player moving abroad: age; personal adaptability; the various personal psychological factors that affect form; the list goes on. It really is a waste of time to use him, or any small group of random players as a measuring stick of quality for the leagues.
It is much more pertinent to look at the European performances of a nations clubs at a given time. After all, European performance, is one of the fundamental measure of a teams success, a fundamental measure of success in the sport and a measure that can be cast Europe wide.
Your previous argument was facile because you claimed that the SPL of the past 20 years, or the Portuguese league of 2004 is in someway analogous to the German League today, anyone with a basic knowledge of football knows that it is a tenuous analogy, at the very best.