2019: Lu Dort over Quinndary Weatherspoon with the 49th pick
Staying consistent with the previously mentioned dream scenarios, the Spurs would probably be picking late in the first and second rounds. That means that they would only have the 30th and 60th picks instead of 19, 30, and 49. That wouldn't have prevented them from selecting Johnson with the last pick in the first round, and it would have saved them from taking Luka Samanic.
Additionally, the Spurs selected Quinndary Weatherspoon in the second round, but in keeping with the dream scenarios, they should have taken Lu Dort instead, who somehow went undrafted. Dort signed with the Oklahoma City Thunder and has quickly established himself as a starter by becoming one of the better perimeter defenders in the NBA. Weatherspoon was worth a shot at 49, but it's clear that the Spurs and every team save for the Thunder missed on Dort.
Fortunately, Johnson increasingly looks like one of the five best players in the 2019 draft class. While San Antonio could have done better, they did a fantastic job of getting Johnson, and bonus points for extending him, giving him a super cheap 4-year, $74 million extension. That deal could quickly become one of the best contracts in the NBA.