If the point is simply to tax people until you have a more egalitarian society, then obviously it is too low.
If the point is to pay for services that people use, the rich are far exceeding the cost of services they use, and subsidizing everyone else by a huge margin.
Simple examples are toll roads, gas taxes, permit fees, ect. SSI is closer to a use tax, but has some redistribution built in. Many cities fund infrastructure using parcel taxes, which approach per capita use taxes as well given that hey are paid by home owners, or often passed on to renters.
Not if their wealth is being subsidized by everyone else and not via their own labor, as in that case, they are using the services of others and underpaying for it. And this goes for anyone, regardless of their amount of wealth.
I think this just collapses into the first case where the purpose of taxes being equality. Unpaid labor/service value is just the rationale.