First you should look at effective tax rates. You will again see that even using capital gain the wealthy pay a higher percentage.
But Capital gains are not a sure thing, they are a gamble on our economy. There are losses and gains but that money is infused into the economy. And any time that money is used it is taxed again.
Ask yourself, are the roads bill gates drives on worth thousands of times more than the ones you drive on? Are the police that he calls worth thousands of times more than the police you call? Are the public schools he has access to thousands of times better than the ones you do?
No that would be absurd and yet not only as a percentage of income but as a total number he has payed thousands of times more to live in the same country with the same public systems as you.
"like two different people paying the same price for the same car,"
Yes there are little variations based on bargaining but price of financing is not the price of a car.