Its not quite this simplistic.....but I understand what you're trying to say. Without getting all complicated, understand that the turbo isnt spinning fast enough to create loaded pressure (boost) until the exhaust offers enough heat from fuel and air flow from rpm's (depending on displacement and impeller design) and the expansion of the air flow from that heat. So just because there's a minimum of around 5 liters of air flow passing through the turbo upon every crank rotation, that displacement isnt whats makes the turbo do much.

The misnomer is that turbos work simply by exhaust gases blowing through them, but thats not accurate. For instance, start your truck and while in neutral rev the engine slowly up to around 3k rpm. If the turbo is spinning simply by virtue of exhaust passing through it in combination of the displacement then you should be making gobs of boost. But in reality you'll only going to see about 2 psi maximum. This is because there's no heat and air expansion coming out the exhaust while revving in neutral. Remember, a diesel engine (at least most of them) are wide open throttle all the time and are only controlled by the amount of fuel injected into them.

So therefor what Gambino is most likely experiencing is a VP which isnt producing the proper fueling and fueling map which is limiting the correct fueling for his engine. Thus little power = little heat which = no turbo boost. End result on a stock truck with stock air box and silencer ring in place is a turbo which cant be heard whistling away.