Athleticism by itself means nothing: it is just the tool allowing players to control a lot of horizontal and vertical space on the court. Athleticism is simply the ability to move your outstretched hands quickly up and down.
And Clayton does have a problem there. His standing reach is the 5th worst at the combine (all four people below him went undrafted) and his wingspan is the 3rd worst (two people with the worse wingspan went undrafted). If you compare him to other small guards in the draft who did get drafted -Fears, Traore, VJ, Cam Jones - they typically have bigger wingspan/standing, by 3-4 inches. So, for him just to be "on par" with other smaller guards he should outjump them by 3-4 inches as well, and be considerably faster laterally. I checked his jumping ability: he is not outjumping them by 3-4 inches.
So, the short answer is that, yes, in general, Clayton will have disadvantages even compared to other NBA point guards. Will he find ways to work around them and be effective? We will see very soon.