I'm pretty sure Paul Graham is not mathematically stupid. the alternative is that he is being extremely disingenuous here. He himself mentioned in the article

I'm pretty sure Paul Graham is not mathematically stupid. the alternative is that he is being extremely disingenuous here. He himself mentioned in the article a threshold of wealth at which the wealth tax kicks in. However his calculations then completely ignore that threshold. no wealth tax is going to take away 95% of anybody's startup company unless their startup company is infinitely valuable.