Requires people to demand Bitcoin for payment instead of accepting other currencies.

And Bitcoin itself can't enforce the physical world, so the same problems that exist today will exist then

What stops it in the fiat world? Bitcoin never claimed to be a solution for every problem to ever exist.

Bitcoin has become more distributed over time since its launch, so that is something tangible that counters your friend’s baseless claim though.

It just won't be used at that point.

Just like when USD fully crumbles and is no longer the reserve, the replacement for Bitcoin will do the same thing as it's predecessor.

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)

“Game theory” in general does not say that one entity will eventually own everything. There are specifc rules in monopoly that work as a forcing function towards the emergence of a winner.

For example there are trade offs between economies of scale and the ability to be creative and nimble.

Typically, powerful anticompetitive entities manipulate governments to protect thier interests and limit the advantages that smaller players have which leads to further centralization in the ownership of assets. The whole point of Bitcoin is to break this typical arrangement by being uncontrollable by governments and other abusers of force by implementing fair rules (proof of work, an incorruptible ledger, censorship resistance, etc).

In short, the rules of the game of monopoly force an outcome. Bitcoin has different rules.

There will always be people who are able to accumulate an outsized supply of the money supply compared to others. However, in a hard-money system, it won't serve to keep poor getting poorer.

This is because the rich won't just be hoarding their Bitcoin. They will want to spend it on things and they will generally be willing to spend more on things they need than other's would, too, keeping ample supply in circulation.

Second, the reason the poor keep getting poorer under fiat is because the rich are insulated from the effects of inflation. They are typically positioned close to the money spigot, so they get to use new dollars before they can no longer buy as many goods, while the poor only get those dollars after prices of goods have adjusted upward to account for the additional supply. So the rich get the benefit of spending the new money when it still has the same purchasing power as the existing supply, and then get the added benefit of the assets they own appreciating in dollar-denominated value.

Bitcoin will flip that on its head. The other assets owned by the wealthy will no longer appreciate in value, because the money supply won't be expanding any longer. And though the poor will still have less money than the rich, that money will buy them more goods over time, instead of less. If the rich decide to hoard more of the money supply, it will only increase the value of the money that is in circulation, because there are less units of the currency available to the market chasing the same amount of goods.