How do you beat Cleveland and GS? You can't compete directly with their main strengths. But these teams do have weak spots around the edges.
Both teams have hyper skilled point guards, but neither team has elite quickness at guard. We already have the quickest guards in the league in IT and AB.
Cousins would give us a similar edge up front. Tristan Thompson and Draymond Green are just too active and quick for Horford and Amir to deal with, but if we could add Cousins , I think we win the war up front too, and by a significant margin.
I think Cousins would make us competitive against those two teams right now.