Melky shouldnt be a deal breaker, although I think he is a fine CFer and will only get better with age and experience.
Kennedy shouldnt be a deal breaker either. I like the kid's poise and his command, but he isnt on the level of a Santana and doesnt have the stuff to ever be on that level.
That being said, Wang IS a dealbreaker. Did he suck in the postseason, absolutely. But he has won 38 games in 2 seasons while keeping his ERA below 4. He is an innings eating groundball machine. And we saw what happens when you dont have innings eaters. Dealing Wang for Santana helps us only for October, and to be honest with you, I am worried about making the playoffs first. If we can align Santana and Wang atop the rotation, we'll hang with anybody.