Might look good at first glance adding a player of his caliber but look at whos on their bench now. A bunch of no name players you probably haven't even heard about.
Anytime you upgrade from an erratic 2nd yr. player to all-star stud, well your team just got a lot better . He plays great D {4x all D teams}, and hustles to loose balls. With Reddick coming off the bench to light it up, the burden of 20+ shots is alleviated.
I'm not sure what above poster means, Butler is a great defensive player.
In terms of talent he is a poor man's Kawhi Leonard, you could definitely win with him being one of your top 3 guys if you surround him with the right people