No. 1: Lonnie Walker IV
If the Spurs have a true swing factor going into the 2021-2022 season, I think Lonnie Walker is that player. His combination of athleticism, length, and skill easily gives him the most potential as a three-level scorer on the roster in my mind. Now that both Rudy Gay and Patty Mills are gone, I don't think it's unreasonable to suggest that the Spurs have given Walker the keys to the bench unit.
Outside of Bryn Forbes, who I believe will only play a limited role off the bench, Jock Landale will be the only other proven shooter coming off the bench. Devin Vassell also has gobs of potential to improve and should receive a fair amount of shots, but it may take another year of seasoning before he sees a meaningful performance jump.
Walker, on the other hand, is primed to make a jump. This past season, he trailed seven other Spurs players in touches per game and yet also led the team in points per touch. Walker was also able to convert on 38% of his catch-and-shoot threes and there is some evidence that he's developing a dangerous pull-up game.
I want for Walker to have the green light from three this season. I think he has the best chance of being the Spurs' best three-point shooter off the bench and, when paired with a stretch big like Landale, could become deadly from all three levels. If Walker can hit threes consistently himself, that three-level scoring potential will only increase.
Depending on how well (or badly) Derrick White performs in the starting lineup, I could even see Walker taking the starting spot at shooting guard if he plays well enough. That being said, only time will tell whether or not that will come to fruition.
Ultimately, if Walker, McDermott, White, and Landale can all remain efficient from beyond the arc, the Spurs' offense could end up surprising a lot of people this coming season. If they can improve their defense compared to last season, the team could shock the NBA and remain in the running for a spot in the playoffs.