The same player can get higher ratings according to enthusiasm but also the opponents. A team with a very strong SF in a lower division can probably play TIE more often, thus higher ratings.
i think it is a think about mentality, many of the top teams take care of an high enthusiam, and very few team play ever tie(which is i think not good, ins ome rare leagues it could make sense if you spot only one rival). Also top team sometime have it easier to reach the high enthusiam because they are in average longer in the cup, and mostly play tie in them.
Consequently, since that team will get higher scores (blowouts & such) , that player plays less minutes which again increases the rating.
I don't see higher rating after blowouts(till fourth quarter the minutes are nearly the same, and i believe he get mcuh energie back in the quarter breaks), and till that the minutes are pretty the same so i don't beieve that will advance. Also this only counts for superior teams in their leagues, and having a good sf doesn't mean that this is true, because you field 5 players.
Maybe even the SF rest longer in a top team, because you have an better backup who will get more minutes.
overall i think with similiar gs and enthusiam the player will perform as good in league 3 then 1 only looking at the rating, for stats i believe league 3 will give him an advantage.