Furthermore:
> Apple doesn't allow side-loading because, well, they're afraid Facebook or Epic would force users to side-load against their will, among other business reasons.
I think "other business reasons" are the bigger issue here. Facebook and Epic wouldn't "force" users to side-load content any more than Apple "forces" you to use the App Store on iOS. It's an available option that you can use at your own discretion.
Apple (unlike Prusa) has painted themselves into a pretty favorable corner. They've made their value proposition immaterial, which allows them to pretty easily deflect any accusations that their 30% cut is out of line. Apple has full control over the goalposts here: they could claim that their cut goes to hosting alone or covers the entirety of the review process.