This here is the idea of DWL, keeping the engine running at more or less a constant power output, as engines operate most efficiently in a narrow powerband. This should be especially true in the case on an engine with a discrete "threshold" to stay in a limited-cylinder mode.

What I'm guessing you misunderstood before is that you thought DWL meant accelerating more on the incline while the suggestion was most likely to accelerate before the incline to build up momentum, and use that, rather than extra engine power to get up the hill.