Here are my thoughts...
Did epic self-inflict these "wounds"? Yes, most definitely.
Do I think the 30% is too much? No, not really.
Do I think Apple should allow apps from outside sources? Absolutely
Just because there would be apps from outside sources doesn't mean that developers would outright leave the App Store, there's a huge userbase there.
Sideloading is and always been for those for are technically inclined and can accept the risk, it wouldn't affect the App Store much at all...
Epic tried direct distribution to android users and it failed with them deciding to go back onto the Google Play store for the exposure
Users own the hardware yet they have absolutely no control over what runs on said hardware, so they don't even have the option of switching to an alternative without paying hundreds or even over $1,000 for a device.