you are hiring Nash because he is an offensive wizard. Melo kills all offensive movement.
Nash + Melo = net losses.
Knicks need a strong defensive PG who can hand the ball over to Melo and stand in the corner to catch and shoot threes.
Knicks have a better chance at winning a championship if they traded Melo for a bunch of high quality role players and left Amare and Chandler as stars.