Slow rhythm is not the root problem here. Joe Ingles played slow and was damn effective. Kawhi and Jokic are slow and deliberate and they one of the best basketball players alive.Cody just plays with a slow rhythm. It hasn't been effective so far but I don't think he can go any faster, Its just kinda who he is.
Cody's problem is his general lack of skills. When you are not good at dribbling, shooting and finishing at the rim you can play lightning-fast and still be equally bad.