Your logic is seemingly correct, but somewhat flawed.
When you step on the gas and open the throttle the cylinder fills more completely from the increased manifold pressure. This increased volumetric efficiency creates more pressure upon combustion. Higher pressures mean the flame front travels more rapidly, thus less spark advance is needed for optimum torque. Likewise, higher pressures raise the propensity of the engine to knock, so if excessive amounts of WOT spark are used the engine will be more prone to detonate.
I realize that direct manifold vacuum to the distributor sometimes creates a "hole" or stumble on acceleration. That is where a ported signal can help you out. But in the absence of a ported signal it is better to have manifold vacuum to the distributor than no vacuum signal at all.
