Correction: Brunson and VanVleet found their way to the starting PG position in the NBA not because they are small but because they are strong and hefty but still quick. Clayton does not seem to be built that way.Brunson
It's actually kind of the norm for smaller guards who are good in the NBA. A lot of them tend to be 4 year players.
But, in general, getting drafted close to 20 at the age of 22 as a PG is just a proxy that after playing all this years of organized basketball the consensus of the NBA decision-makers is that you are unlikely to become a quality starter in this league. The GMs are often wrong evaluating 18/19 year olds but they are typically much more on the target looking at 22-yo prospects. Clayton can still prove them (and me!) wrong but the chances of that are what...10%? 20%?
The smart betting money would be on him being a career back up.