Newcombe was a great volleyer. I'm certainly not putting Tanner with him, but there is a big gap between Newcombe level and so so or average. Tanner vs Ashe I think is pretty close. Ashe, if he was on, could hit you off the court, besides his serve and volley. Like Tanner, not always consistent.
Ashe said that about Sampras? Was it early on or after he peaked? Like with Laver, I would disagree. Still, it's a learned opinion and shows how much they can differ. I have no hesitancy calling Sampras a great volleyer. IMO, a clear level below the creme de la creme, but meets the level of my idea of great.