Firstly, it’s no more luck based than any other method. There are less than 3000 billionaires in the world. If there was an even pseudo-reliable system to become a billionaire, there would be more than 0.00004% of the population who’ve managed it.
And selling a popular video game is just as much “exploiting a supply/demand gap” as any other method. You have an effective monopoly on an asset that people want.
All that to say, I’m pushing back on the “massively oversimplified,” because it’s not, it’s just counterfactual.
I wouldn’t have minded if the OP had said “the overwhelming majority of billionaires got there by exploiting the working class.” That’s just as “massively oversimplified” as what they did say, but isn’t objectively false.