The Zucman tax is absolute minimum of what's required at this point. It should be higher, it should be progressive, and it should start at lower levels of wealth. Moreover, in the future it should be applied globally and yearly.
I propose a simple, practical test: ask anyone with more than 100 million dollar or euro what their exact wealth is. The difference between what they say and what it really is, that can just be taxed away. It's going to be more than 2%.