I'm going to chime in with my simple thoughts on the DDP and Disney Dining in general.
The DDP was initially invented for one reason - the very same reason they invented Magical Express: to keep you on property. That was THE reason. If they prohibit you from renting a car, you can't escape. And if you've pre-paid for all of your meals, you won't try to escape and eat off property or go to Universal. It really was that simple.
Then, the bean counters saw that they weren't MAKING enough money on the meals being consumed by DDP-ers (note, I said "not making enough" because they're not losing a penny on those meals...they're just not making as much profit per plate as they do on OOP-ers. Keep in mind that it costs them less than $10 in food/labor to serve your $35 TS entree. And don't get me started on the profit margin built into desserts.), so they've gradually increased menu prices (to get more money from the OOP-ers) and adjusted the cost of the DDP at a slightly faster pace.
At the same time, they also slightly reduced portions and the quality of food to lower costs. Eventually, those graphed lines will come extremely close to each other, or actually intersect if they keep up the current pace - thus rendering the DDP a "wash".
Meanwhile, OOP-ers are picking up the tab for the earnings lost on DDP-ers, and even more so for Free-DDP-ers.
As for the inability to get a table in short notice, that's attributed to all of the factors. Since the advent of the DDP, table service meals have been ushered into the spotlight. When I was a kid in the 80s and 90s, we didn't eat at a table service restaurant in all of the numerous trips to WDW. The line of thought was "Who eats a fancy dinner at Disney World?" I'm sure many people thought like that as well....and/or they were venturing off to eat at a $9.99 buffet on 192 (like we did).
So, with attendance increasing over the years, table service restaurants being more prominent and known, the encouragement of guests to eat at them via the DDP, and then the seasonal influx of guests eating TS meals when they're giving them out for free....it all adds up to full tables all the time, which is exactly what Disney wants. As long as all of the tables are full, they don't care who's upset.
And honestly, as someone else implied, Free Dining isn't really to blame. They're merely robbing Peter to pay Paul. You can either book a room for up to 40% off and pay for food...or you can pay rack rate for your room and get food for free. Plus, when they throw in mandatory extras like the PhotoPass book, you'd actually come out money ahead with the Room Discount and smart spending OOP.
Lastly, the DDP is truly only a "deal" if you would have normally ordered everything that comes with the DDP if you were paying OOP. So, if you always get a soda/tea, full entree, and dessert...then yes, the DDP is a deal for you. But here at home, when we go out to eat, we always drink water and never have room for dessert. Therefore, the DDP includes far more product that we'd ever buy normally. And when we add up the cost of the food we'd buy OOP, it totals a sum far less than the cost of the DDP.
The DDP is a "perceived" savings, based only upon the (essentially) prix fixe menu you've been assigned. I will admit that we succumb to the marketing gimmick called the DDP, but we do it solely for convenience and to create a thoughtless experience while we're there. We know we're being taken, but I also know I'd NEVER pay for a drink or enjoy their desserts if I was swiping my own credit card at each meal. We'd be eating like [something that doesn't eat very much].
Take this for what you will. None of what I've said is opinion. It's all factual. (It's actual. Everything is satisfactual). However, my one piece of opinion....
They should reserve a % of tables (say, 10-15%) every day, all day, for walk-ins or guests who book that morning via concierge or Guest Services. I know Disney would HATE to do this, because it means they don't have every table filled in advance, but it would be a nice gesture to the locals who just want to have dinner in Epcot for a night, and to those who don't know if they'll want steak or spaghetti 6 months in advance. This one little thing would solve 99% of the griping with the DDP (except for the lesser quality food, but people would get over that if they were at least given the opportunity to eat it).