True, there are many assumptions about the game, but that's what they remain, assumptions. (just as mine obviously and from a relative rookie at that) Some people mention a reset at start of the season, but many more are experiencing it mid season. And of course players will perform differently in a different league or lvl with different opponents so there'll always be fluctuations. Ratings and quality are nice, but I'll prefer cold hard stats with a direct link to a result (goals) preferably over more then 1 season. But you might be looking for a while to find one. My last ST I bought, had scored 59 goals in 50 matches when I bought him. So far he's scored 7 goals in 5 matches. I'ld be surprised if he fell back dramatically allthough it's still early to say.
Btw, that's also the main shortcoming of the android app I use, no match stats! Hmm, should be a good one for the ask the devs...