The people who say they don't see NBA potential in him are: 1) lacking knowledge about what constitutes NBA talent; or 2) lying.
We've been over this. XJ has good athleticism (even in the NBA, he's at least a plus athlete as a backup guard). Good size. He's a good defender. Good dribble-penetrate. Adequate FT shooter. Average shooter.
He doesn't shoot for volume and isn't a great distributor. But he's also limited by the fact that he's not surrounded by shooters and teams just pack the paint against us, taking away his best skill. You wouldn't be able to do that in the NBA because Xavier could dish to 1 of literally anyone else (including an average NBA big these days) who can shoot the 3 and make you pay. Most critically, Xavier is barely 20 years old and the door to the league doesn't automatically close when you're 22 and out of NCAA eligibility.
TJ McConnell makes $3.5 million per year, scoring about 7 points in 21 minutes per night. He's not particularly good at anything but he tries hard. And he's almost 28 years old. You really watch Xavier Johnson and think he can't be at least that good in 2 years?