That's why I specifically called out futures trading. From [1]:

> In the financial markets, options and futures are examples of zero-sum games, excluding transaction costs. For every person who gains on a contract, there is a counter-party who loses.

[1] https://www.investopedia.com/terms/z/zero-sumgame.asp

That quote is misleading. He's talking about perceived price. The actual price of an equity is the price at which the execution occurs. And for every execution there are two sides, hence the zero sum game is the only game in town.