I agree. Markkanen, himself, is a former #7 overall pick. If I had to guess, right now, Markkanen is a better player than Mobley and, if that’s the case, he should start. That doesn’t mean Mobley won’t be the better player, but he has work to do, both in the weight room & on the court.
This is no different than the Chiefs not starting Patrick Mahomes his rookie season and having him watch Alex Smith. The NBA is different in that more than one guy will play at a particular position over the course of a game. Mobley will get his minutes. He shouldn’t start until he proves himself better than Markkanen.