The issue isn't really if 30% is "fair", its that the market has no way to find out if it is because apple have forced devs into their app ecosystem by delibera

The issue isn't really if 30% is "fair", its that the market has no way to find out if it is because apple have forced devs into their app ecosystem by deliberately keeping iOS browsers slightly worse than native apps (no push messaging or background processing). So there is no viable way for an alternate store, with an alternate fee structure, to run on iOS devices.