In my experience, the decline has been real, not fabricated. I will agree that food at WDW is definitely much better than in the '80s, when WDW was truly a culinary wasteland.
Then, there was a period in the late '90s, when it was really good. There seemed to be a real effort to offer unique and interesting menus and choices that might not be found elsewhere (and we live in NYC, so that impressed us!). For example, Maya Grill, when it opened, featured a truly unique and exciting Nuevo Latino cuisine. We eagerly looked forward to our meals there, which featured foods we had previously only tasted in our travels in Latin America. A couple of years later, however, the menu had been "dumbed down" so it's now just another steak and chop house. We quickly lost interest.
Spoodles is another example. They used to have lots of fun and different items on their menu. The diversity is now gone and it's much more like a typical chain restaurant. We'll eat there, but the excitement of something unique is gone.
Perhaps the most ridiculous decline was at the Boardwalk Bakery. For years, we've picked up their breakfast burritos for a quick breakfast. They always came with a small side of salsa. When we were there last November, the change from salsa to small packages of ketchup happened while we were there! At the start of our vacation, one got salsa with one's burrito. A stop there later in the week and, lo and behold, no more salsa -- just packaged ketchup! We've noticed other changes at the bakery as well -- they used to have a different flavor of crumb cake every day. Then it went to just plain crumb cake. Then it went to something that resembled a big muffin.
While we still enjoy the table service restaurants immensely, the rest have had noticeable (and not fabricated) changes, that have not been for the better.
Folks may say, well WDW is just giving the people what they want -- they want lots of food and don't really care about the quality, they want chops and not Nuevo Latino cuisine, they don't mind ketchup packets, etc.
Okay, that's fine. But, there's definitely been something lost in the race to mediocrity, IMO. Again, mass market cruise lines seem to be the model -- not much variety, nothing real tasty, but lots and lots of food included in the vacation package.