Are leagues weighted?

[endersgame]

In my European adventures with some teams playing in smaller leagues - e.g. Ajax, Celtic, Standard Liege etc. I've noticed that my teams seem to struggle against sides from some of the bigger leagues, particularly the EPL. It doesn't seem to matter if I am playing a Cardiff side during their injury and form crises I will struggle to beat them. This is not simply due to them having better players than I do, because none of these players would get on my bench nor is it my tactics because because I won European trophies using the same tactics with the likes of Arsenal, Dortmund and Roma. Or am I just imagining it? :O