> pretty uncommon for exchanges to do all their market making directly
Point is, in real finance, it's pretty uncommon for exchanges to do any of their market making. Largely to ensure they can project confidence in crises. Market makers blow up. Exchanges shouldn't.
> Do exchanges in real finance even have long term customer deposits?
Not really. They used to! (A hundred+ years ago.) But we learned that an exchange blowing up is a hell of a lot worse than a bank or broker. So most systems segregate the functions. (It's also not great to have an exchange making markets and thereby having a vested directional interest.)
Point is, in real finance, it's pretty uncommon for exchanges to do any of their market making. Largely to ensure they can project confidence in crises. Market makers blow up. Exchanges shouldn't.