For "big" eaters, I suppose it's a great deal. People who would eat multiple meals in one sitting.
But what it really shows -- is that QS v. TS has nothing to do with food quantity. There are many $10-$15 QS meals that are bigger portions than $30 TS meals.
The difference in price comes down to food quality, location, setting, and extras.
I suspect if you took the characters out of Chef Mickey, Crystal Palace, etc -- you'd end up with a buffet worth QS pricing.