I don't agree with this, as a developer and a consumer. As a consumer it is extremely nice that I don't have to deal with all sorts of exotic and different payment gateways. Some accept Amex, some don't. Some try to store my card without my consent, some don't. Some make it really obvious that not being charged during a trial period some don't. Some payment gateways are buggy, slow and frustrating and some are really good. As a consumer I bloody hate that and I love iOS and Apple for the fact that I can securely put payment methods behind Apple Pay and then know that I can do any in-app purchases via an already established and well working gateway. No faffing about with some other shite.
From a developer perspective I don't see why anyone should use the AppStore as a distribution channel to a huge market and completely circumvent Apple's cut when clearly they are offering a lot of value by making this possible in the first place?
For example, my VPN I can either buy a license by going to their website and go through a 5 minute checkout process or I can do a 5 second checkout via the iOS app. The first one goes 100% to the VPN developers, the second also means that a cut goes to Apple. Sounds fair to me, because I literally purchased a VPN in a moment where I didn't have the time of going to a website. I was abroad, I was on a mobile and I had limited time to get quickly a subscription so I could use the VPN and I would have not bought it if it wasn't for the ease and speed which the app allowed me to do. This was only the case because Apple does such a diligent job in keeping it so sleek. Without Apple Pay I would have not bought that license and they would have not lost 30% of the sale, but effectively 100%.