Melo is definitely not useless on defense, but I still say Melo's D is below average due to a gross lack of consistency. When he plays man defense, he often allows for his man to roam fairly freely to whatever spot on the court he chooses. When playing on ball defense, he often allows good shooters too much space, inflating the opposition's shooting percentage. In a zone, Melo is normally a big liability, seemingly forgetful of where his zone should be or indecisive on which man he should body up. He's also suspect on switching his mark with teammates, normally left in the dust on pick and rolls. He has the tools to be a hard nosed defender, but with the expectations for him to perform on offense, I'm sure he struggles to muster enough legs to play immaculate defense the entire game through. #7 is one of my favorite players, but that dude just doesn't have the constant vigilance on the defensive side of the ball to be considered an elite defender in my opinion (for all that matters) as of yet.
I wish I had a player that I could call a Carmelo Anthony clone for sheer entertainment (imagine if you had a Melo player playing in a Patient offense), but I feel like an Artest (don't forget he can spot up shoot respectably) would help me win a championship. I like the versatility a well balanced and talented defensive player offers in this game a lot because week to week, you'll know that he will be effective at slowing down whichever player you want him to at several positions. I hate being hung out to dry when I scout an opponent and he has a big who can shoot further out and I don't have a big that can cover him on both the outside and the inside. Being able to stay in M2M defense, from what I've gathered from forum study is a huge plus in limiting the opposing AI coach's in-game adjustments, and having a player who can guard multiple positions helps keep you able to play that way.
I wish I was in a better league so I'd have more credibility. :P