I think Young is the better player by very slim margins. Seems to be closer to a natural athlete than RJ, I can more clearly imagine a world where Young's frame fill out and his natural, effortless shooting stroke of finally paired with some defensive intagibles.
They kind of remind me of the dilemma that the Sixers were facing when deciding between Ben Simmons and Brandon Ingram. While I do think they made the right choice as Simmons is more likely to turn into an All-Star player than Ingram in my opinion, but the argument was valid in questioning whether Ingram's skill set was more easily projectable to be successful at the NBA level than Simmon's game.
Kind of the same thing with RJ and Young. RJ may be a better basketball player in a vacuum, but he doesn't easily slide into what you traditionally imagine a 2/3 to do, he's got more playmaking ability which while impressive, I think could clash with primary ball-handlers that already have the playmaking covered.
With James Young, all I'm asking him to do is come in when your number is called and get buckets. Use that length to defend and board as much as you can, but when you catch that ball behind the 3-point line, I don't want you to drive and kick, I don't want you to probe the defense and maybe squeeze out an opening for a floater, I want you to shoot the ball. That's why I'm taking Young with the final roster spot.