They're having completely different seasons because of their respective roles. Wade is the sidekick to Lebron's alpha male, while Melo is the alpha male on his team. As a result Wade only shoots 14.8 times a game while Melo shoots 21.8 times a game. Further Melo plays 37 min a game while Wade plays 33. Wade is a better all-around player than Melo hence the higher rating. Melo is having a better offensive season than Wade and he's already better than Wade on offense, so what else needs to be increased?