It is probably needless to say this, but…
Disney and other amusement parks (and, well, businesses in general) don’t offer discounts to benefit you, the end customer. It is to benefit themselves. So, TiW is offered not because they want to give you an opportunity to save money, but because Disney sees it as a revenue-generator. They expect that a lot of people will put the TiW cost (initially, pure profit for them). Then, as a result, you will get your discounts…but they also know that for many people, now that you are getting the discount, you will more likely end up shifting more QS to Table Service and end up spending MORE than you would have without the TiW discount. Furthermore, even if you are going to eat at the same number of TS establishments, with a discount, you are more likely to spend a little more (splurge on a drink or dessert, etc., that you might not otherwise).
So, in the end, Disney is using TiW as a means to get you to spend more and you would have otherwise by offering you a “discount”.
That isn’t to say you can’t benefit from TiW or any other discount…but the calculation should be based on how you ACTUALLY would intended to eat, not modifying your eating habits because of TiW. If you find, based on your planned spending for food, that TiW ultimately saves you money, great! You beat the system. You become, to Disney, much like those who pay off their credit cards off each month to credit card companies.
I’ve seen the same at other places. Like, at Cedar Point, for example, you can “pre-pay” for food…but it is questionable whether doing so makes financial sense. CP limits what food you can get on that plan, and you may end up paying more than if you just waited and bought the food in the park.
Similarly, McDonalds sends out coupons. If you look, MOST of the time those coupons don’t necessarily save you money, but just allow you to spend MORE money than you otherwise would have by getting MORE food than you would otherwise order for cheaper than their regular price. (Oh, look! Buy one Big Mac, get one free! Except…well, I usually would just order a McDouble, so really I go from spending $2 for two sandwiches to spending $3.50 for two bigger sandwiches.)