Brees and Vick cant both throw the ball. If its a passing play, it will have to be Brees or Vick throwing the ball. If Vick throws the ball, then Brees is not throwing it. Therefore it is one less throw for Brees. It makes no sense to ever have Vick throw instead of Brees. It makes even less sense to use Vick purely as a WR or RB, he has no NFL experience at those positions. He's not a better WR than Colston or Moore. He's not a better RB than Reggie or PT. He's not a better QB than Brees. There is literally no use for Michael Vick on the Saints team.
Coach Payton specifically said that the Saints have the lowest level of interest in the wildcat offense out of any team in the NFL. The reason why? "That's just because I want Brees to be getting the snaps all the time."
its not a poor argument.