He and Burks are getting roughly the same minutes this season. Gordo and Burks are better defending the 2, RJ is better defending the 3 (a little extra size/physicality).
Corbin is trying to keep players' roles simple, so it's unlikely we see Marvin playing much at the 3. There's definitely a trade-off there, and reasonable people can disagree on the relative value of giving players consistent, well-defined roles v. allocating minutes to maximize on-court talent. I personally like Marvin at the 4, and would like that to continue. I'd like to see Gordo more at the 3 with Alec though. I'd be pleased if RJ's and Alec's minutes from the last 3 games were swapped (Gordo with 36, Alec with 33, RJ with 27)
It's probably also worth pointing out that getting between 24 and 32 minutes isn't a disaster, especially since Alec is still getting plenty of opportunity with the ball in his hands leading the second unit AND ample opportunity off-ball with Trey and Gordo closing games.