Chandler's path to starting in the NBA isn't going to be improved by playing here vs playing in the actual NBA. He's either going to be skilled enough to play there or he's not. A second year here playing 35 games in a college system won't do for him what 82 games plus summer league will do for him, if he goes to the NBA.
Your second point is absurd. No one cares about Michael Jordan because of what he did at North Carolina except for North Carolina fans. His legacy was written in the NBA. Same with Larry Bird, Magic Johnson and even Bernard King. We love King for what he did here. His most known and important basketball legacy is his dominant scoring and MVP level play in New York.
Pete Maravich is probably the only player I can think of with a huge legacy based almost entirely around his play in college. When your dad is the coach and you get to shoot 90 percent of your team's shots, it works that way.
This nails it. College legacies are primarily local issues, even for college players of the caliber of Jordan, Magic, Bird, and Jabbar. These guys are associated by the public with the NBA teams they helped win titles and got to the Hall of Fame playing for. Even Maravich, nationally, is more known for his stint with the Jazz than LSU, as college ball was entirely a regional sport in those days.
Regarding Chandler, he appears to be a mid-late 1st rounder on most boards. Staying in college for another year, even for big NIL money, carries with it far more risk than reward, which is limited to possibly raising his draft stock. The risks include regressing in performance, which would have the opposite effect on his stock, and worse of all an injury.
A first round contract and being one year closer to that all-important second contract, plus the ability to work on his game full time are things he would lose by staying here another year. As you said, how much more is his game going to develop in a college system as opposed to a full season with pro coaches?
Chandler was always going to be a one-and-done. It's time to move on and concentrate on the things that will continue the growth of the program - recruiting and the transfer portal.