We have two of the best scorers in the NBA. We don't have to be finding ways for them to score more points - they can make it happen.
I don't know if it's a defensive assistant, a defensive coach, or just defensive roleplayers, but the team has to do a better job of finding players who can get those stops. The Celtics built an offensive juggernaut with their big 3, but they also had players who were good on defense (and nothing else!).
Every championship team has those players who are elite defenders but aren't much on offense. Ben Wallace, Kendrick Perkins, Trevor Ariza, etc...