Hey inline300 . . .

Let's do a little math and see if your intuition is true.

First let's assume two-inch 'tall' venturi at the base of our theoretical carb(s) - this will make the math easier - because it's just calculating the area of a cylinder, which is what we'll need to hold constant at 'any one moment in time' when comparing setups (single, dual, trip).

So let's look at a one barrel setup with a 1.42" venturi. The volume of air in the this setup at any one moment in time is 3.2 cubic inches:
(radius .71 - height 2)

Now let's look at the velocity of this theoretical carb flowing on top of a 216 at wide open throttle @ 140 CFM (not unlike a Carter W1):
(radius .71 - CFM 140)

The air is flowing at some ~144 miles per hour.

Now let's compare this same setup with a two carb setup that consists of two theoretical carbs that are exactly half the size of the Single setup. A one inch venturi size will give us two columns of air that are 1.6 cu inches in volume each (again at any one moment in time):
(radius .5 - height 2)

Now let's look at the velocity of this twin carb set up on top of a 216 at wide open throttle @ 140 CFM (70 CFM through each venturi):
(radius .5 - CFM 70)

The air is flowing at roughly the same ~145 miles an hour as in the single carb setup.

So I agree with your analysis, most duals and trips are a less drive able setup because the venturi size of the carbs selected is perhaps two big (Roger Huntington warns us about this in his book). Look at what happens when we use two Carter W1s on a 216:
(radius .71 - CFM 70)
Velocity is cut in half at the same airflow.

But what if we assume that the stock manifold is restrictive and that the 216 engine can actually flow 20-30% better with the dual:
(radius .71 - CFM 80-90)

In spite of the added volume (160-180 CFM) the air is flowing at only ~83 to ~93 miles per hour though the two venturi.

This decreased velocity will impact drive ability because of the lower vacuum signal - which will impact throttle response and port vacuum pull on the vac advance in the dizzy. Without some tuning adjustments the dual W1s will likely be lean and the timing late at low RPM (as Hoyt points out).

regards,
stock49

[Linked Image from 49fastback.com]