If I could I WOULD trade Mo for Turner straight up. But that is because I would start Gibson and Turner would fit because he would be an upgrade defensively from Mo.
I am not sure Turner will end up being a better player than Mo long term, but for team fit I would do it. Mo does one thing will, shoot the ball. That is a very important skill to have in the NBA. If you have a guy like that as a coach, your job should be to get him open looks. We never really did that with Mo. Watch Ray Allen, he needs a ton of picks to get open to shoot it...same for a guy like Reggie Miller back in the day, tons of picks to get open. Mo shoots the three ball BETTER than both of those guys. Think about that for a minute.
Gibson is a top 8 CAREER three point shooter, and yet he sat on the bench?!? Parker is top 10. Mo is around 30th in career three pt percentage. THREE of the top 30 ALL TIME on the same team. Why not set these guys picks to get them open looks?