Kawhi Leonard is not better than George Hill, who can score, is playoff tested and one of the best defensive PG's in the league.
George Hill is decent, but he's not even in the top half of starting point guards in the league. He has good defensive technique, but he cannot guard quick point guards. All you have to do is look back to Nash and Dragic abusing him in the playoffs by blowing past him with ease.
Kawhi Leonard is a more valuable defender than Hill already. Kawhi Leonard can guard 1-4. He's guarded Chris Paul for stretches and he can also guard Dirk Nowitzki and Lebron James. A guy you can put on the team's top perimeter player regardless of position is a luxury to have. And he can hit the corner 3, can rebound, and plays with a lot of hustle and intensity. And his upside is great. Ask R. C. Buford and Pop would they rather have Hill than Kawhi and you'll get