The point of a 90% marginal rate isn't to increase tax revenue, it's to discourage high incomes that are economically and socially harmful. If you don't believe that's a problem then policies to address it won't seem logical.
Even if it is, and even if your point is true, that's not what the GP said. They said taxing rich people a higher percentage than poor people is "more efficient" (whatever that means in this context) and a "[more] fair system," and immediately followed it up with the 90% anachronism.