Increments of gain versus multiple factor. So I'm considering an additive level and not using the value as a multiple. Your take .33 and multiplying as compared to additional to make 1.33 instead.
But in general the concept you state is correct. If you would take the 600 series to the CM and compare similarly sized models, you would find they are close the three times the cost. It would not be outlandish to say the increment of a 1/3 gain or 1.33x improvement in performance between them. If you also to the CM to 800D series of similar size, its again not to far off this mark. The 800D series do have models that are far greater in size to achieve certain goals that were never even approached on the lower lines. Its part of the business model to provide something for everyone. I don't use the Diamond series as its a recent refresh and the current 600 and CM series are still waiting for their next.
You can see this business model being used to different effect in Kef, Focal, Monitor Audio, Dali, Dynaudio, and others. You would also note those who walk to their own drummer and have different ideas about speaker lines. Wilson would be kind of big, bigger, biggest, and bigger then biggest. But they do plan in this manner for their lineups and in consideration of what their competition is doing.