Yes. All the desserts were out and ready.
At our party, they probably started running out of some of the desserts at about 9:00-9:15. No doubt about it. BUT, 75% of the people were there by then.
One thing to remember is, when they run out of one dessert, they replace it with something completely different. So, if you don't grab something right away to try it, you might miss it--there is p-l-e-n-t-y of everything though. But if you fill up and grab everything you want on the first trip, you might be unable (full/sugared up) to try something equally or more appealing later. We were victims of the latter. When we go in October (hopefully), I'll know to pace myself.
They never ran out of desserts, not even at the end, but the choices did go down towards the end. At our party (and it will vary by who is at which party), there was always plenty of fruit and chocolate covered strawberries. Lots of cookies too. The ice cream never ran out, but the toppings dwindled at the end--much to the disappointment of my son. The drinks remained constant and full--they ran out of nothing there.
Personally, I plan on being early again. I liked being able to get great pictures in front of the castle before there was a line (or anyone in the background). I liked seeing what all the choices were, but I'll go slower (and I know what I don't like now too). I like being completely done before the show so that we truly get to enjoy the show. It's not like waiting in crowds to see the parades/fireworks. It's relaxed and enjoyable. It's quality time enjoying your family--very nice down time. No one is pushing. You aren't "guarding" your spot. You aren't basically doing nothing. No one is trying to get you to buy over-priced junk for your kids. And the snacks are already paid for.