First, I wasn't comparing him to Duncan, merely replying a posted comment.
As to your question. There is no financial advantage, at least for the first three years of his new deal, for the Spurs to sign him to an extension this summer rather than a new contract next summer. There are, as has been discussed in many previous threads on this subject, significant advantages for the team to wait until next summer. My point, in those threads and this one, is that waiting comes with risks. Many choose to dismiss those risks, but I believe that they're real and that the Spurs would be well served to avoid those risks. I said so long before the details of the new TV deal were known, and I feel even more strongly now that we know the actual numbers.