Would you be willing to pay 30% more? Why not let people choose how they wish to pay. If you like that UX and are willing to pay for it, app developers should be able to offer it along with cheaper alternatives.

One of the things the App Store protects against is abusive practices like making it difficult to cancel a subscription. I wish there was some way they could protect their customers and allow outside payment services.

FWIW, the streaming services I want easy unsubscribe options are typicall $5-$8 / month and yes, I would pay 30% more for a better experience.

As a counter point, I always avoid subscribing via the app as the prices are higher than if you subscribe via the website. Google One has this where you pay more to use the apple method.