Both, and not just in a manner of speaking.
The legal system is organized to support private property and entrepreneurial activity. For instance, one can organize a corporation, borrow money from an investment banker, do business, go broke, and have no personal liability. At every step of business, rules governing business elements like depreciation, capital investment, and so on are in place. It isn't just the final tax on income or estate taxes that aids the rich getting richer.
If Joe Blow, factory worker, borrows money to fix his car so he can keep getting to work, and the car is still unreliable, he'll lose his job and will still be fully liable for the loan. True, he could file bankruptcy, but that might not help him.
Now, it is true that the ability to get rich and stay rich is one of the reasons remarkable innovation and aggressive expansion occurs. Michael Bloomberg made his huge fortune by supplying financial operators with something they very much needed: up to date financial information in ready-to-use forms through the Bloomberg Terminal. It was a high end financial data delivery service.
He didn't just become worth $58 billion dollars by delivering newspapers. He was a partner at Salomon Investment Banking, and as a partner accumulated $10,000,000 which he used to start his new business.
Fortunes require a foundation of money, from somewhere. You might be broke, but if you have a simply fabulous idea that will turn a profit, some investment banker might risk a few million bucks om you, and if everything goes well, you end up quite well off. If it doesn't go well, you don't. It went really well for Bloomberg.
Bill Gates didn't become the richest mortal to walk the earth on the basis of how wonderful his Disk Operating System (DOS) was. Dos and several other Microsoft products were rammed down the throats of consumers by highly anti-completive methods. I don't know if you remember this, but once upon a time when you bought a PC it would ALWAYS have Microsoft software on it, pre-installed. Later, it would have Windows, then Internet Explorer, something you couldn't get rid of for love or money. It was crappy software, but that's whaat was in the bundle.
Deals were made with equipment manufacturers. That why people had to put up with generally crappy Microsoft products (some of which, like Word and Excel, were good). If you didn't want Microsoft, you pretty much had to buy an Apple, which was more expensive.