Fundamentally, it ignores whether freedom of movement should be infringed in such a way. One can currently sideload an APK on Android, but what's stopping Google from taking the same hard line as Apple?
Note: I am using the hyperbolic analogy above for rhetorical reasons; I don't think Android phones are perfectly analogous to a scooter. We use Android at work precisely because of Apple's lockdowns, and while I actually like the OS well enough I think I would find it frustrating on a personal phone.
A better metaphor might be renting a home. Imagine if you could only fill it with furniture and appliances that have been approved, and you can only park certain types of cars in the garage. You could always move, but then you have to buy new everything.
Sideloading is free.
Given that the application store can be changed to blacklist a certain app, it is not unlikely that the next step is similar changes to the apk installer.
It should also be noted that there are no guarantees that signature checking is optional in all future builds of Android. While there are differences between the iPhone and Android business models, they should also not be overstated. My personal guess is that they will drift closer over time rather than farther apart.
Resistance due to money (and effort) that would need to be spent to migrate to Android is not the sunk cost fallacy.
TL;DR: "sideloading" for iOS = Free: no. Convenient: no. Possible: yes. Out of reach of most people: absolutely yes.