You don’t need any statistics to know that, just basic common sense. Finance is using money to make money. If you have more money, then you have an advantage over those who have less. Democracy is when the weak can band together to overpower the strong. Obviously those with advantages are going to use those advantages to retain their privileged position.
What keeps this from getting ridiculous is two things. First is politics and the law. As more gets known about financial techniques, laws can be passed to curb abuses. For example, accreditation for investors was created to curb unscrupulous salesmen from selling worthless products to the naive. Without the ability to pass laws regulating financial trading, markets would be a lot smaller because only the biggest dogs could compete.
Secondly, the fact that being rich makes you lazy. Finance is a zero-sum game, every dollar you make is a dollar someone else loses. In any closed-loop system, entropy eventually reaches the max and activity grinds to a halt. Meaning that without new wealth coming in from somewhere, someone is going to quickly hoard all of it. But with new things, new innovations, new ways of trading, comes the ability for those with merit to beat those with means.
This is why you’ll always be able to make far far more money starting a company than you ever will trading.