Sorry abd, I always appreciate your unique perspective but I think you are clinging to the term "volume shooter" a little too much. The two most relevant associations with being a volume shooter are:
1 - That the player is unable to fit into a gameplan unless he is the focal point in the offense...so if he is going to contribute, he has to be getting his shots. I think Willie demonstrated last season that isn't the case. He fit in where he could get in.
2 - Its a nice way of saying that a guy has shot-making ability, but lacks the ability to identify good shots from bad. Again, I don't see this applying to Willie at all. He seems to be a relatively efficient scorer and I disagree with your claim that Blake helped him in that regard. When Blake was in the game, Willie was almost only a spot-up shooter. But when Blake was out of the game (thus creating open offensive sets), Willie had the room to get higher percentage shots by driving.
Bottom line is I just don't think the volume shooter tag applies well here. By your very loose definition, any guard who is a good scorer is a volume shooter. Steve Kerr, for example, was not a volume shooter. In fact, I'm trying to figure out someone who is a high-level scorer that isn't a volume shooter?
I know your intention wasn't to say anything negative about Willie, and I for one don't think you have. But I think your honest motives have maybe caused you to defend the term a little too vigorously. Just call him a go-to scorer and leave it at that...that's all you're really saying anyway...