Nope, but that is what I used to think also, the vacuum should be highest at idle.
A lean fuel charge burns slower so you need more spark advance, which is what happens when you have a lot of vacuum.
THere is no vacuum advance at WOT only at idle or cruising.
We're talking a street car here. He's not running the engine at WOT. Even at the initial WOT, you get vacuum advance until the manifold vacuum drops. At that point, the RPM's are up a bit and the mechanical advance takes over. If you ran your vacuum advance hose directly to the intake along with say 10 degrees of initial timing, you would have somewhere around 25-30 degrees combined at idle. Way too much and bound to ping on you. With using the proper ported vacuum outlet on the carb, initial stays at 10 degrees at idle, but, then advances as soon as you open the throttle. Sure, the vacuum will drop off if you stay in it, but, that doesn't last long in normal driving. On a drag car, or, an engine with a radical cam, you don't even use a vacuum advance, because you don't have enough vacuum to work one properly. Gas mileage will suffer without one, but, that's not a concern on a drag car. They just use a distributor with more mechanical advance range and slightly more initial timing. All it takes is for you to hook up a vacuum gauge with a T-fitting to the proper port on the carb, and watch the timing light as you work the throttle to see how that works.