I was wondering about that too. EPCOT definitely has less capacity in numerous ways, but I don't think the Magic Kingdom has less. The rides that were shut down have been replaced by others (20,000 was replaced by two rides). I suppose there could be a small decrease in capacity with the Stitch theater closed and a few other small things gone (like the keel boats), but I think the Seven Dwarfs/Little Mermaid combo would make up for that.
They absolutely failed to keep up with the attendance increase, though. And if you want to argue the quality of some of the new rides is less than what they replaced, I'd agree with that, but it's a separate argument from capacity.