That depends on what we're talking about jeebs. Are we talking about production, or talent/skill? Talent/skill wise, you're right. KD is just a notch below Melo. But production wise? They're not even close. KD is just a much more complete player when it comes to being efficient. But I don't think the ratings are trying to reflect efficiency (think Wins Produced (Wp48), not PER or NBA EFF)...I think the ratings are trying to capture a player's skill and talent, and they are accurate in that sense.
Think about the ratings. 99 Med shot? What does that mean? To me, it means a guy has the talent to score from midrange. But how does that actually translate to production? Wouldn't a 40 Med shot be more accurate, to reflect the actual shooting percentage that player makes from that range? Then we would know, "OK, so if he's open, he'll hit, say from 38-42% of his shots from this spot, and if guarded, that will go up/down depending on the defensive rating(s) of the player(s) guarding him. This would give us more precise data when using teams. But 99/87 etc. ratings don't tell me accurately enough about how efficiently a player is going to score from a given position on the court. And as a coach, I would know exactly where and how to use Melo to get the most out of him...