If that is the case, then it worsens the problem. Because now there is even more of an incentive for restaurants to overcharge. If the majority of your customers are on DDP, then they do not care about prices. Put whatever exorbitant price you want on your menu. Those fake sales only make the GM look better.
The incentive for the DDP is to make the perceived value look better to the consumer, as opposed to the actual value.
Food quality at WDW has consistently gone down since I have been attending. And while dining costs were always high, the current pricing levels exceed that which is normally expected for captive audiences.
Also, for your explanation, that would work for WDW owned restaurants. How are privately managed places compensated under DDP?