Disney did offer a Deluxe Dining Plan up until 5 years ago, which covered 3 meals and 2 snacks per day. That still required some counting, because Signature restaurants counted as 2 "meals," but not as much as the current Dining Plan. If Disney thinks they can make money on a plan like that, it may return.
Guaranteed last-minute reservations would be more difficult, because if a restaurant is full, it's full.
I do not like having "2-credit" restaurants, because it looks like prices at those restaurants are increased to justify making them cost more credits. However, if all restaurants are a single credit, the more expensive and unique items will simply disappear.
My family stopped getting the Dining Plan when our kids became Disney Adults, because the mostly-vegetarian meals we eat typically cost less than the price of the plan and we went to fewer character meals. It's clearly not for everyone. It doesn't bother me that it's not ideal, though, since it is clearly optional and (other than my complaint about 2-credit meals) it doesn't affect me if some families choose to use it.
When we went using the dining plan, I felt a little pressured to maximize the value by eating one of the most expensive entrees and of course always getting a dessert, and that’s just not how I eat. So sure, you can work hard to get the value out of it, but I’d rather eat what I like without thinking about that.
In its current form, the dining plan would never work for us. DH doesn’t drink and I rarely do, so the inclusion of alcohol makes it so we can never come out ahead. We also are not big dessert people, sometimes like apps, and often will choose the cheaper entree. I guess I just like more flexibility, especially on vacation.