Duke walk-ons are typically not that great largely because there’s a small pool of candidates and they typically can’t keep up with scholarship athletes. At UNC or State, you can find a number of guys who are almost as good as the scholarship players, or who at least won’t be embarrassed on the same court.
It’s just tougher at Duke.
There have been exceptions of course, notably Bruce Bell, who stepped up in the Foster years and became a critical part of the team in (we think) 1977, when Tate Armstrong was injured and Steve Gray had two devastating mistakes as point guard, both in tight games: in one, the ball bounced off of his leg out of bounds.