"Athleticism" when people use that word I have to try and see if they are speaking in code or not. I will assume you are not. I realize an NBA comparison isn't exactly an apples to apples comparison, but think about the top 10 NBA point guards only Chris Paul is your prototypical old school point guard. The game has evolved to be about spacing, yeah, a prototypical pg would make things easier; however FM can make it work with JB. Think Jake Sullivan.
Defensively, he will never be a up in your grill Aaron Craft type. He simply won't. However, he is a smart kid with a wealth of knowledge to tap into. He will incrementally get better, not over night, you will see progress.