There is absolutely no doubt that the essential part of the performance issues from the brain and the hands of the player. After all, the instrument does not play itself. On the other hand, the player cannot produce the sound without the physical instrument. It is not an illusion at all. It's fun to say radical things like this, along with the other unsubstantiated striking things that Hal says that grab people's attention. For example, no one has "proved" that you play what you hear. The premise that you can and do play whatever you hear is, IMO, nonsense.
Take a person who has never played the DB. Now, let that person listen to Ray Brown. Give that person a DB and ask him to make that sound. Of course, something quite different will come out. Now, do you really believe that what comes out is exactly what the novice heard when he listened to Ray Brown? I sure don't.
Ah, some of you will say that Hal shouldn't be taken so literally. Sorry, but he speaks it literally. Of course, what we, as players, produce is very much affected by what we hear in the sense that it is affected by how we analyze, integrate, and incorporate what we hear. No doubt, that's true. To say, however, that anyone is wrong who claims that he has trouble playing what he hears is hyperbole.
I really don't find sweeping, extreme points of view helpful in teaching. The truth is that performance is a human endeavor. The instrument does matter to the extent that it, as a physical device, allows the player to easily and effectively express his creativity. You can't have one without the other.
I also agree with the sentiment that many make too much of the particular choice of instrument, strings, etc. While one should be cognizant of the dominating role of the "human aspect," to eschew the influence of the physical apparatus completely is folly.