He needs to get stronger, develop his outside shooting. He can do that in the G League as a member of a team playing in an empty stadium with no one watching on TV with teammates who are completely and only focused on their own personal goals, vs team goals and hope he plays his way into the league. Or, he can work on developing those same skills playing in front of 20k plus fans, on National TV with teammates who are more focused on team goals than G league players while furthering his academic education and allowing himself the ability to mature in a college environment vs a quasi training camp.
Its a no brainer unless he hates the academic side of college.