Dev here. That 30% cut is actually great. It means for a flat rate, I don't have to worry about hosting, payment processing, getting my app in front of millions of eyeballs. I don't have to worry about the exchange rate in Tokyo and what that means. I get to spend far less time administrating my business and more time writing code, which is what I want to do. It's probably also cheaper than what I would pay if I did do everything piecemeal and manually, not even counting my time and what that is worth.
Everyone advocating for alternate payment processors is really only supporting billion dollar companies. The only devs who would ever use something like that are those who have a full on dedicated dept to run it (aka Epic, Spotify, Microsoft, Google) and are trying to squeeze every last dollar out to bump the shareprice. You aren't defending small devs or one person shops who don't want to spend all day administrating a business to save $5. I'll gladly pay Apple and Google to do that for me.