The one thing a democracy cannot allow the rich to do is convert their associated wealth into political power. The proper tax rate for the very rich is 51% of their income with no loop holes for the 51% of taxed income. It’s a psychological amount that reminds them they didn’t earn it. It’s also a leveraging amount that keeps them from amassing too much political power. We also tax gains on their assets as they accrue at the same 51% no loop hole rate.
We get rid of money based elections as well as tax havens. We tax capital flight enough to dissuade it. We make it a crime for private entities to play one government or municipality against another for tax breaks. We also institute a wealth ceiling by specifying an absolute amount beyond which all gains will be confiscated. We also tax dynasties out of existence. The probate rate should be at least 90% of assets and income, no loop holes no capital flight. One of the best supports for the livability of a society is making sure the children of the rich cannot escape its prospect through birth.