IMO the attitude of the team improved dramatically when Rondo was traded. The ball began moving around on offense, everyone started looking for the open man. The ball pounding ended.
The defense was vastly improved, because the team decided to hang their hat on defending. Why not? They had nothing else yet. The team was able to create a small identity, with the Bradley, Smart, Crowder crew.
Enter IT!... exactly what the C's needed at the right time. The Celtics prior to Thomas coming to the team, went through minutes where they would have trouble scoring the ball. (lack of a talented consistent scorer) They needed exactly what Thomas brought to the table. If IT went to another team that didn't care about defending... and with players similar to himself, he would not see the success he see's with the Celtics.
Pure talent is nice, but in Professional Basketball Chemistry is King.