As a second rounder, he would not be guaranteed any money, and while the fact that this particular draft class is weak might mean that Jax gets drafted where in other years he wouldn't, it doesn't mean that he would get a contract. It is highly unlikely that an NBA team is going to look at Jaxson and say "yes, you are a relatively weak defender, passer, and rebounder compared to the players we normally sign, but because the class of 2024 is weak, here is a multi-million dollar contract."
I still think he should stay in school and work on improving his skills. Aside from that, he should watch how Ritchie plays the game. Someone with Jaxson's physical skills who played as hard as Ritchie would probably be a lottery pick.