Sorry not intended as snark, I do think you raise a good point, and may yet dim my enthusiasm for pure consumption taxes. But would be good to generate more examples to think through.

One unfairness is people who have spiky incomes, like a guy who repeatedly builds companies & sells them off, 4 years on ramen & 1 big payoff -- it does seem unfair to put him in the tax bracket of those with 5 times his average income. I have an idea many countries would let him smooth this out already, but don't know the details.