I wonder if they changed it? Or if the batches vary? Mine was absolutely not "mainly a cake," it was mainly icing. There was a teeny bit of cake in the middle.
I've had it 3 times. It was always the same. I also had the lemon dessert and that one had just a tiny bit of berry filling, like a spoonful. My Grey Stuff was more cake and cookie than grey stuff every time. Sounds like you got a bad one.
It also doesn't have a buttercream cosistency to me. It is more mousse like...has the same "air bubbles" structure of a mousse.
Here is a good review of it:
https://www.buzzfeed.com/crystalro/...st-and-it-real?utm_term=.ccK67VKk7#.vk0dPm8nP