I know, but he took a significant amount less to play for the Spurs over the Heat and the Suns. Each of the latter teams were offering deals for close to the full MLE over several years. He signed with the Spurs for roughly half the amount because of their le prowess.
Then why even talk of opting out? If he's not going to sign with a contending team for the MLE, then he may as well just rot in Minny for the remainder of his productive career. No contending team will have the CAP space to sign him to a MAX contract and he's no longer a player that can single handedly make a team a contender.
Also, it wouldn't cost Phoenix both Amare and Marion. If the Suns happened to bite the bullet and traded Amare for Garnett, it would likely be an Amare/Banks for Garnett type deal.
This deal gives them a frontcourt rotation of Garnett, Marion, Diaw, Thomas, plus a few late-1sts. Throw in Nash, Bell, Barbosa and Jones on the wings, and you have plenty to contend with.