I totally agree with you.
My players overplayed last week, due to injuries, 6 fouls and overtime. Yet, the ones with a better stamina not only didn't drop, but even improved their GS.
This is very disturbing indeed, because I don't know if their GS won't be as high provided they play less in the week. E.g. Jacoby has received an improved GS with 83 minutes played, does it mean that he won't get to 9 with the standard 50 - 70 min. or is this actually an advantage (yes, 50 - 70 is optimal, but if stamina is high you can push a little further and this will be just as good ?) with no nasty side effects ?
Mystery ...