My observations so far is that teams do a MUCH better job re-signing their stars that are still in their prime than previous versions of NBA 2K. And I have yet to see any blockbuster trades that didn't make sense.
For example, LeBron gets re-signed by Cleveland in the couple MyGM sims I've done. Have not seen Durant, Westbrook, Lillard, Harden, etc. move from their teams. However, I have seen older stars move/not resigned.
On the flip side, Rajon Rondo, for example, was not resigned by the Celts. Also saw Jokim Noah not resigned by the Bulls and sign somewhere else after a couple years of simming. But both of those guys are past their prime and their skills start to decline after the first season or two of progression. Al Jefferson is another, he got traded by the Hornets to the Lakers, pretty sure it was for a pick and Xavier Henry I think.