3s outside of gimmick comps has always been rough for boxers. If you play a melee/ healer 2s comp you can do well in 2s though. Primarily because the other team can't CC you into the ground. 3s is just harder because it hits that balance between CC and one shot mechanics. In 5s though the one shot will return.

I suppose 3s could work if you played 3s REALLY well. Like not stacking, having your CC chains worked out and not overlapping cooldowns. The problem will always be that and positioning though. We get trucked.