Apple doesn't need to monopolize payment to centralize subscription cancellation. More importantly, Apple's fee structure prefers cheaper trashy apps over expansive to produce quality apps. I hope users will feel the difference with an overall better app selection.

Example: Apple takes a flat 30% fee while Stripe takes (IIRC) 0.3 + Y% (when Y much lower than 30). So a cheap app will pay the same or less with Apple, but an expensive one will lose a lot with Apple. I know not all expensive apps are quality ones, but at least this model will be economical now.