Why do you think Melo won't play 'possum' again? I can't find anything reasoning. I think he can and will if he's bottled up as such, the Spurs play the best team defense in the league outside of Miami and they effectively neutralized Melo, forcing him to be productive in other ways. It didn't help that Melo's open looks weren't falling either, so he recognized he needed to get going in other ways.
Brooklyn however, could NOT neutralize Melo, neither by team or individual defense. Melo missed a ton of open looks he should have made, but in general he could get his shots off.
The only thing I do agree with you is that YES, teammates tend to stop playing hard defense when the offense only runs through 1 or 2 people -- they stand around, looking uninterested instead of moving around, setting picks, boxing out -- that's on the coach to illustrate.
....But the notion that Melo won't ever defer again is not in any way true.