Do you think that he wouldn't have done what he has done if there was a wealth tax in the US?

I think the answer to this is a resounding Yes, he would not have done it. Tesla and Musk is the perfect example of why a wealth tax on capital is insane.

Tesla market cap is 750 Billion, but the profit is 500 million, and the stock owners that haven't sold have realized $0 profit.

A 1% wealth tax on Musk's 200b ($1b) would be 4 times higher that the profit of the entire company.

Under the current system, the moment he cashes out any stock, he will have to pay taxes on his actual profit. The reason we income instead of wealth, is that wealth can go up and down without the owner seeing any benefit.