these are things the vast (and I mean >98% VAST) amount of general computer users are not capable of understanding and should not attempt regardless.

That's the problem, isn't it? It's actually fine that you can't do this, because the average user is too stupid to be able to do it safely. That's the Apple ethos. That's their justification for disallowing sideloading on iOS, however flimsy it may be. I don't care that my grandma doesn't know what doing this would mean. I'm not my grandma, dammit. I own the computer, let me do whatever I want with it!

I use Little Snitch, which absolutely can block traffic to Apple’s domains.

That's another thing I should've added to my list: find basic system utilities, like a drive cleaner, firewall, or alternative terminal emulator, that aren't paid products.

I work at a small, locally owned, computer shop. We order Mac parts and install them all the time. I’m literally doing a MacBook Air screen replacement tomorrow morning, and we’re not AASP. I don’t know what you’re talking about.

Has Apple finally pulled their head out of their ass and removed parts pairing? This is great news!