It's his defense that might hold him back. He's played about 1/3rd of his games at 2B this year, and 2/3rds at 3B including all of his AAA games. Last year was around 50/50.

His 2B fielding percentage would put him around the middle of the pack(if not a little lower).
His 3B fielding percentage is awful. Of 22 qualified major leaguers, the lowest fielding percentage is 0.941. Rylan is at 0.917 for the year and 0.915 for his career.

If he can improve his defense, he looks like he'll have the offense to make the league.