The Milwaukee Bucks gave up a more skilled player for a lesser one. That much is fairly objectively true–as overall basketball players, Michael Carter-Williams is better than Tony Snell. The trade was more concerned with fit than talent.
Since Middleton got hurt, the Bucks have needed someone to start in his place. Rashad Vaughn got two shots to prove he was capable in the preseason, but unfortunately he failed to do so. Malcolm Brogdon could be an option, but rookies generally don’t start on good teams, and the Bucks prefer to use Brogdon more as a point guard anyway.
Jason Terry is a proven player, but he might be too proven to be relied upon as a starter at this point. Jet will play an important role on this team, but asking him to start just isn’t a good plan at this stage.
That left MCW, who might’ve been a decent option considering his proficiency at cutting without the ball. He has the size to guard shooting guards, but his lack of outside shooting meant he would bring the amount of shooters in Milwaukee’s offense down to one–an experiment which failed miserably last season.
The Bucks needed an athletic wing who could shoot and play defense. They first tried for Ben McLemore, and when that didn’t pan out they instead worked out this deal with the Bulls to fill that hole.