You're right that the claim that "being a billionaire requires exploitation" is massively oversimplified. But the situation you've described is essentially winning the lottery. Yeah, you put the time into think of, and execute on an idea, but everything else, from having the time to work on a possible flop, to it being a hit with 300 million people is ultra luck-based. 1000 people could do the exact same thing, and 1 might hit it big. It's gambling.

A more accurate phrasing of the original statement is: the only way to reliably amass billions of dollars in wealth is to exploit a supply/demand gap to the point of unsustainability.

A small business that operates with integrity, prioritizes the wellbeing of their society over their profits, doesn't price gouge, and doesn't discourage healthy competition will never become worth billions. They will always lose to competition that is willing and allowed to forego ethics for profits.

So 100 people could try your strategy of making a game that goes viral, and none of them are going to do it, most probably won't even make a profit. But then 100 people could try the strategy of exploitation, and they're going to reliably turn a profit. We allow a society where exploitation is a good investment.

Regardless of what people think of Peter Thiel he says out loud exactly what is wrong with late-stage capitalism: competition is for losers.

You are talking about Minecraft level success and even that took many years of success and being bought by one of the largest companies in the world to reach that many sells.