A couple things: 1) we don't need Gerald Green; 2) we haven't even seen much of McDermott due to injury and the FO is not going to trade a rookie, whom they gave up two picks to get, for a 1 year rental player who may or may not even be as good as McDermott; 3) Mirotic played the 3 BY DESIGN LAST NIGHT. That was not out of necessity. Yes MDJ is out but that gave Thibs the opportunity to give Niko an extended look at the 3, something they had been trying to do for weeks.
A guess what? He knocked it out of the park! Not only did he prove he can guard on the wing, he proved that he can even take a very good wing defender in Ariza off the dribble. His defense has improved DRASTICALLY over the past month. It's the main reason why he is seeing even more time now. Before he used to be pushed around by everyone down low. Now, he is bringing physicality and holding his own in the paint. Before he used to shy away when opponent was flying toward the hoop at him. Now he is getting in their face. Case and point his run down and block of a streaking James Harden on a full court fast break play.
At this point, this team is as complete as you can get for a championship contender. There's depth at every position, skill at every position, the offense can play inside and out, and the defense can shut teams down in stretches to seal victories. The team is on a total roll (13 wins out of last 15) and there's no reason for a friviolous trade that does nothing to improve the team overall.