Rather, I think that the argument is sloppy, lazy, and frankly relies on a severe lack of imagination and rigidity of mind from those that present or accept it. Thus we should stop parroting it as it makes for a very boring discussion.
Instead, maybe there is an interesting discussion to be had as to whether Google maintains control using Google Play Services? Technical aspects of how a consent mechanisms could work relative to bootloader unlocking? The viability of Apple’s offerings in terms of better privacy and payment UI if something like Fortnite “broke free” and started a competing store? All this sounds endlessly more fun to read and contribute to compared to: “I am content with the status quo, it serves me well, and I see no reason to discuss this further with you freedom zealots!”.
I don't think GP meant that it wasn't technically possible, they were saying it isn't possible for this switch to exist without some popular apps eventually getting almost everyone to flip the switch and negate the whole point of having a switch.
I don't think I agree with them because Android already has this switch and I can't think of many apps that lots of users would want to sideload, except for Fortnite.