It's mathematically proportional, but not morally proportional, not for someone who thinks proportional income means more to those with less, which is what you are saying you feel about the current tax structure.
I agree with you. 10% of gross income to the working stiffs mean a heckuva lot more than 10% to someone making millions, and it's because of what you end up with. The $50K example guy ends up with $45K. The $30M guy ends up with $27M. You have to budget everything, where you live, what you eat, what you drive, what you wear, around an extra $5K at that income level. At $27M? You don't have to budget anything, you can still live wherever you want, drive whatever you want, eat wherever you want, etc., etc.