The last sentence is irrelevant.They're both 7 footers. G/F are effective for longer in their careers than centers. Only 5 of the top 36 oldest players in the NBA currently are centers. Big men break down much faster.
You're forgetting playoffs. Tatum played in 339 vs Ant's 329.
And it'll be 2 more seasons until Ant is the same age as Tatum when he won his first championship.
Jamal Murray, another top tier guard, played virtually every game his first three years in the league. Since his fourth year he's played in about half the Nugget's games. There are more Murrays than Tatums.
I decided to drill down a little more on your contention that smalls last longer than bigs. The average height in the league is now slightly over 6'6". In 2023-2024, of the 25 oldest players in the league, 16 were 6'8" or taller.