Exactly.

90% millionaires and 10% billionaires means the billionaires have 99.1% of the monetary power.

That sounds like a systemic problem with democracy, not wealth inequality. You want to put people in charge of making decisions both for themselves and for others, but you don't trust them to make those decisions properly. The issue here isn't so much the influence of money on public discourse as the ever-increasing divergence between the myriad things the government involves itself in and the naturally limited qualifications (and standing) of the average voter regarding each of those complex issues.

The problem of money purchasing political power can probably be solved without eliminating the concept of a yacht.