Hill is a good player, and is not a liability handling the ball, but has never shown that he can use his skills to get other players shots or otherwise involved in the offense. He's in no way selfish, but his court vision makes Parker look like the second coming of Magic.
If you want to talk about doing the job of a point guard on offense, from your list Beno, Stoudamire and Vaughn were better at it than Hill.
Vaughn's problem was that he couldn't shoot for squat, and so the defense could sag off him with impunity. But he still knew how to run an offense.
Mighty Mouse was actually doing a very good job at point until Pop, in one of his "bench Bowen and let Kobe get loose" moments, insisted he stop passing and start jacking up shots from everywhere.
Beno was easily the best backup point guard the Spurs have had, but of course we all know Beno's problems were all between the ears.
, Brent Barry was a better point guard than Hill. And if Speedy's half a season counts, him too.
Having said all that, finding a better point guard than Hill is definitely NOT a priority need for the Spurs.