I'd say Zappa was serious enough about the shallowness of humans, enough to take him to the grave with understandable disgust.
The man was the greatest humanitarian in our lifetimes, expressing himself in a humorous, crazy, upsetting manner that alienated 99% of his potential admirers. He took no prisoners and paid the price for his courage. In my perception, he put a mirror in front of many of us, asking the question - Is this what you really are? Shallow and a piece of excrement?
He took no prisoners and didn't spare my idols either for an understandable reason. HE LET GO OF EGO by then. The man is a legend and whilst it's somewhat sad, he had to forego words and express feelings in music instead. For that, we all are better off - without having to find a mirror.....