Holmgren's impact on winning
Holmgren has been a two-way force for the Thunder right out of the gate, probably even better than what many expected this early on in his career. He's currently averaging 17.6 points, 8.0 rebounds, 2.6 assists, and 2.2 blocks per game (6th in the league).
Holmgren is already the second option on a Thunder team (behind Shai Gilgeous-Alexander) that is a top-four team in the Western Conference. Rookie of the Year typically isn't impacted by how many wins your team has due to it usually going to lottery picks that play for bad teams. For instance, Wembanyama is on one of the worst teams in the league, the Spurs, who are 3-16, last in the West and have lost 14 consecutive games.
Wembanyama has been putting up good stats: 19.3 points, 9.7 rebounds, 2.6 assists, 1.3 steals, and a staggering 2.7 blocks per game (2nd in the NBA). Despite that, Holmgren has the advantage over Wembanyama due to making an impact on both ends for one of the best teams in the NBA which might convince voters to vote for him over Wembanyama.
Holmgren also has the advantage of having Gilgeous-Alexander and Josh Giddey set him up in pick-and-rolls and find him for easy baskets. Wembanyama doesn't have that luxury of playing with an All-NBA guard the way Holmgren does with Gigeous-Alexander, which takes immense pressure off his shoulders and opens up things for Holmgren due to Gilgeous-Alexander's elite scoring ability that draws two defenders to him.