If that were the case the criticism of Paul Graham's reasoning would be wrong to begin with because the only people paying it would be the people who do get most of their income from investments.

Moreover, your proposal doesn't actually work. If corporations don't pay the wealth tax then rich people just put their assets into corporations that they control but don't formally own (there are many ways to do this). But if they do then ordinary people with ordinary retirement savings can't be spared, since it doesn't change your finances to have the companies your retirement savings are invested in give you lower returns by the amount they pay in wealth tax than to have you pay the wealth tax out of the returns.

We don't know, actually. If the threshold for "wealth" is set to be >100k, then we are.