It cant happen with bitcoin (or truly hard money) because that rich guy (or govt etc) will still need and want “things”, like running water, garbage collection, fast cars and everything else. And the only way to get that is to part with bitcoin for goods and services. And of course, all the people supplying those things need things too. When the currency is finite, it can never easily be hoarded like your friend suggests as it needs to be spent.

The only reason it happens today is because OF the nature of fiat. It can be printed/created with no proof of work, and the “rich” can basically get all the things they need by spending newly created money, therefore not parting with any of their existing money/assets. And then apply the compounding rules…

Also if you read the rules of monopoly, you’ll see that it says something along the lines of “if the bank runs out of money, just write the value on some new random bits of paper and use that as the money” (just like real banks)