There are two types of starting PGs: the high scoring ones (the majority of PGs right now) and the floor generals. Collier has very few tools to become a high-scoring PG: he has no jump shot and he can't play above the basket. To have potential as a starting-level PG he should show the flashes of superior floor general skillset: think Chris Paul, Tyrese Haliburton, Trae Young, Cade Cunningham, LaMelo Ball... All of them flashed the passing/playmaking skillset in their rookie years far above of what Collier currently has. In fact, the point guard is the deepest position in the NBA right now: there are about 15 All-Star level PGs right now and more star PG prospects (Demin, Traore, Jakucionis) are knocking on the door in the next draft.
Again, he is not a bad player as a PG but his potential rather points to a solid backup role in his future (unless you anticipate his explosive growth in several areas). And backup point guards are cheap and easy to find as Chris Dunn undoubtedly knows.