Butler is a top 10 scorer and top 10 defender.
Jae is a role player scorer and a top 10 defender.
As others have said, Butler's ability to create his own shot and get to the rim/free throw line are what make him a far superior upgrade to Crowder.
One is a role player, and one is arguably a top 10 NBA player given the strength of his two way game.
Curry, Harden, Durant, Lebron, Cousins, Davis, Westbrook, PG, Thompson, Leonard. Somewhere after 10 Butler fits in with guys like Lowry, Derozen, Lillard, LA, Wall, Paul.
Outside of Harden really, who in that top ten isn't a great two way player?