The only reasons Castle is ranked higher than Carter are because he played for a more prestigious program, he's 3.5 inches taller and 2.6 years younger.
Castle has him by 15 pounds and 0.02 inches by wingspan, but Carter plays much bigger as evidenced by his elite "event creation" (2.8 blk% and 2.9stl % which in the NBA would tie for 30th and 1st respectively) and all-time guard rebounding (23.7 drbr % to 12 %; the former is equal to Holmes and greater than Clingan and Filipowski by .3 and 1.1% respectively).
He's also a way better 3-point shooter (37.7% on 6.6 3PA/G to 26.7% on 2/2 3PA/G).
We've seen teams constantly overrate the former's (high bust rate) archetype and underrate the latter's (high hit rate) archetype for these same reasons.
The Spurs have been beneficiaries with the likes of Hill, Murray and White. Others include Caruso, Podziemski, Nembhard, Mann, Melton, Brogdon, Brown and Quickley.