This is an interesting discussion and one that I suspect is occurring on many internet sites.
We also just came back from WDW. We weren't and haven't been crazy about the food. What has changed for us, though, (and it doesn't matter what the cause is) is entree size and in particular, beef entree size. Now before you get crazy, understand that we dine out frequently in the NY metro area. Portion sizes do change but not as dramatically as we have seen at WDW. My DH ordered a beef tenderloin at Chef de France (your fave, Bicker, I know) and was appalled at the size. It was literally a golf ball. Now normally speaking, that works for me because I'm a smaller person. But for him, after walking miles throughout the park all day and really not eating a regular meal, it was far too small. Luckily he supplemented it with an appetizer (rubbery escargot) and a dessert. This pushed the price far higher than the quality given (our perception, not others, obviously). On the DDP it would have been fine. A la carte it was a travesty. Interestingly enough, our tuna entrees (my son's and mine) were huge. Yes, tuna is better for you. But it's also quite expensive to serve and the portion difference was amazing. The reason? I have my doubts that it's heart healthy. I suspect that more people order beef on the DDP so they cut the size of the entree to avoid waste and to increase the profit.
Can I prove it? Absolutely not. Nor do I intend to fight about it. It is what it is. We did, however, cancel the rest of our ADRs and eat offsite for the remainder of the trip. This was my husband's decision. And truthfully, I've never seen him riled up about food before. But taking into account size and quality (and I know the latter is personal), we felt that a la carte ordering was a huge rip off. So if we choose to eat onsite in the future, we'll do the DDP. It's a lose, lose for us basically because for us the quality and quantity has declined.
As an aside, I read your Spoodles review, Bicker. When I was last there, the lemon chicken was just that. Lemon chicken. There wasn't a caper or spicy black olive in sight. I'm glad they got back on track. It was one of my favorite entrees at Spoodles.