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We will agree to disagree, then. You can formulate elegant proofs, or you can observe the real world.
The entire point of having an intake manifold vacuum in the first place is to control the amount of oxygen in each firing cylinder. That's all. Pumping work is a necessary evil for a basic gasoline engine. Anything else that uses (power brakes, for instance) engine vacuum is trying to make the best of the situation.
That being said, adding any sort of load will increase the amount of required work. Engine accessories, underfilled tires, headwinds, and even ersatz air pumps made out of non-firing cylinders will increase the amount of required work. The pumping work consumed by the DCD deadbeat cylinder will have to be considered as a component of the work required by the engine, correct?
So, even considering that intake manifold vacuum will in fact become lower, the DCD engine is expending even more fuel that is not actually pushing the vehicle forward. To push a vehicle forward at some constant speed, a set amount of required power must be met by the engine. The engine must provide enough available work to meet this requirement. Plopping the pumping work of one or more dead cylinders, onto the work required to push the vehicle forward, and all the other work required by the vehicle, will not help matters.
Discussions, about balancing AFR or redefining lambda to be some other variable or drawing comparisons between DCD and lean burn, will not change this. I simply don't know any other way to point this out to you, christofoo, other than to say to you and other doubters, that you should actually go do DCD-type experiments with your engines.
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