You can’t tax the super-rich. They are the ones who collect the taxes.
If the problem is that the super rich are too powerful, have too much control over the state, then they just won’t allow any tax or law or regulation that would threaten their wealth or power. Any wealth tax that does get passed would be something that they are able to avoid, and would likely hit upper middle class (professionals, entrepreneurs) hardest, and move their wealth up.
When oligarchs have control, state apparatuses are their tools, not the people’s. Politicians are employees of the oligarchs. The legal changes they make may have some secondary or temporary benefit for the regular people, but the net effect will be to benefit the oligarchs. If a politician tries to do otherwise, he will be fired because he’s not doing his job.