Your formula is the basic income of an exchange, but now exchanges have more ways to make money, especially with top exchanges. They can collect fees from listing, IEO, Lending.
Yes, you are right. The formula in my article is basic. This is just one of the articles about exchanges that I want to share. I will share others later. In addition to the profit-making method you mentioned, I think market making is also one of the ways for the exchange to make money