I think a better comparison would be android, not the Mac.
Let’s face it, the majority of people using the Mac are usually more tech savvy. Not all of them, but most of them. And most of them can figure out how to download applications outside of the App Store.
With android, 99.9999999% of people are probably just using the Google play store, which is why the majority of applications are still available through it.
I don’t see this being any different with iOS, especially with how confusing and restrictive everyone already knows apples going to make it to sideload.
If you don’t offer your application in the App Store, you’re going to basically have no chance of survival.
Even from the big companies, you’ll see Facebook moan and groan all day, but will they remove their apps from Apple‘s App Store? Absolutely not.
Also, the Mac App Store is a terrible comparison to anything because the Mac App Store is terrible in the first place.
Even Apple doesn’t use the Mac App Store for everything, the trial version of Final Cut Pro, betas of Xcode, all of that you download from the Apple website, not the Mac App Store.