Your problem is that the distribution of people and incomes amongst the percentiles is not linear. You need to re-do your thought experiment but with 1 guy in the 90th percentile earning 1bn, 10 guys in the 80th earning 1 million, 1000 guys in the 70th earning 100,000, etc. etc.
For me the point that "Ponty's" 'example' ignores is that the price of beer isn't a tax. It is a price for something bought. Whereas tax is actually one side of a coin. (pun alert!) The other side is the social decision to give money to the poor and give more to the poorest. The basis of this is to ensure - ideally - that everyone can manage to live in at least a reasonable state of comfort, health, education, opportinity, etc.
On one side we give more to those who have more need - poorer, have economic disadvantages due to factors outwith their contol, etc. On the other we tax more from those who have a higher surplus about what on average people need to live in a way that avoids them being hungry, cold, ill, etc. In effect they have a higher amount that can contribute without being in any real difficulty.
This in turn means that - via education, health, ability to get to or from work, etc, can then do work from which 'wealthy' people can make some profit and that then aids them to be in a situation where they can afford to pat more tax whilst *still* being better off than many.
If you want a decent civilised society graded taxes and social provisions go together.
Thus the shallow daftness of the Trussonomics approach on a social level as well as in terms of finance. Basically, their right-wing-think-tank fantasies make no sense from any angle - except for a few ultra rich and powerful who care only about themselves and invent beliefs that flatter their convenience.
