Here's a crucial mechanism that Paul Graham did not mention:

With a wealth tax using his calculation, the higher your returns, the lower the comparable income tax would be. If your returns are 10% you'll pay $1 on $10 capital gains which is 10% and you end up with $109. Conversely someone achieving a mere 1% cap gains would be essentially taxed for 100% of his return.

With income taxes it's usually the opposite: the more you earn, the higher the tax bracket you will be put into.

Somebody like Paul Graham surely has higher than 10% capital gains, otherwise he'd not be exactly a great investor.

Personally I'm against wealth taxes, I think capital gains taxes are a much more appropriate and fairer tool. I also think taxes in general are way too high, if you are part of the middle class and add up everything you pay in taxes, fees, insurance, duties and whatnot you can end up losing 70-90% of whatever you earn. It's extremely hard to actually accumulate wealth for the vast majority of people.