Definitive Reason 2: Combination of Dominance and Versatility
Like Russell, Duncan sacrificed scoring for team success; he just did so shooting significantly better from the field and line while averaging 19 points per game for his career - a number higher than Russell's best season average. Again, this was Duncan holding back. Don't believe me?- check out Duncan's absurd performances in playoff losses, often keeping his team afloat when no one else could.
More impressively was how he scored. While not quite Shaq or Wilt, Duncan possessed vastly underrated strength, which he complemented with an offensive repertoire and footwork rivaling Olajuwon, Kevin McHale, and other low post masters. Even late-career Duncan, despite limited mobility, had just enough strength, counters, and technique to evade even the best defensive bigs in the NBA as Nazr Mohammed and Tyson Chandler articulated for the Player's Tribune.
It's this combination of strength and skill that made Duncan arguably the best of them all. He truly was the perfect hybrid. His strength and low post dominance surpassed the Garnetts and Dirks of the world while his fundamentals gave him versatility the Shaqs lacked.
This was best evidenced by Duncan's ultimate counter, the signature bank shot, but also visible from Duncan's numerous game-winners from the mid-range as well as a certain game-tying three Suns fans would rather forget.
Duncan did this as the team's de facto point guard -- hear me out. The Spurs' base offense during his prime was a play called four-down, which isolated him on the low (mostly left) block. Except isolations for Tim Duncan were seldom actual isolations. He demanded a double if not triple-team every time he touched the ball, and sometimes even before.
This led to tons of passes to assists or secondary assists that never showed up in the stat sheet, much like Duncan's underrated ability as a screener, which generated plenty of easy scoring opportunities.
People forget that Duncan's prime coincided with 2001-2002 rule changes enabling the return of zones and paint-packing strategies for the first time since the 1940s, reintroduced in part to limit Duncan's (and Shaq's) domination.
While Steve Nash's "7 seconds or less" Suns marked the beginning of the modern NBA 3-point shooting and spacing revolution, the Spurs did not catch up until the latter half of Duncan's career. These rule changes and Duncan's team-first offensive approach combined with the Spurs' lack of spacing prior to the beautiful game mean that Duncan excelled as a low-post big man in arguably the most difficult era to do so.