Cousins would have been useful if healthy and if Denver had made the WC Finals. He could defend Marc Gasol. I don't see anybody on Milwaukee he could guard. Cousins was atrocious against the Clippers when healthy.
Durant, on the other hand, will be useful against the Bucks. But he needs to battle on the glass which he really hasn't this year.
If I were Kerr, I would do everything I could to make Giannis uncomfortable. I would rotate Iggy, Green, and Thompson on on him. I would pressure his dribble. I would have guys cheat help in his direction but not double. I would double late in the shot clock. I would have guards look to poach outlet passes to Giannis. I would have Draymond keep pushing the pace to make Giannis run. Kerr's staff has nine days to game plan Giannis.