Provided there is no competitor in the store they already use, and that you as the developer do not bankrupt and consequently offer your app nowhere.
And yet trivial little alternatives like idk maybe you ever heard of Steam did actually happen, or the entire Android ecosystem itself when there was already an immense Palm app ecosystem that was like desktop apps where you got apps all manner of ways from physical sd cards to web sites to various curated stores. Or idk Epic, over a single app. They are back on the traditional stores now only because they called everyone's bluff and were suceeding, so the old stores caved rather than be seen to lose to someone so much smaller and newer, even in a small way that was more appearance than material.
There is no such thing as unthinkable. It's all not only thinkable, it has all actually already happened before and multiple times.
If something seems unimaginable, that only says something about your imagination not the reality.
This is very unlikely to change without regulatory intervention.
F-Droid is not doing too bad. And yet, the vast majority of people will never ever use it after Google Play implenents their developer verification scare screens.
None of your examples succeeded in an environment that was even remotely as hostile, neither Windows nor Palm could have done what Google does today, without risking a fatal user backlash.
It's one thing for something to be thinkable and imaginable. Of course you can imagine Google Play getting dethroned. It's just so incredibly unlikely to happen without regulatory antitrust intervention that it is pointless to consider seriously.
But as time goes on and software tools become more powerful, there is just not much moat. I don't even mean AI, I just mean the ordinary power annordinary computer and the gobs of highblevel languages and frameworks and automation that just grows and grows all the time. It's not that hard to port an app to a new platform, or a new distribution mechanism, or a new clone source for an existing platform and distribution mechanism.
Big universal things with 100% capture get replaced overnight all the time. Everyone switched from MySpace to Facebook in like an hour one day. Other things like my Steam example took longer but they became at least an equal player, a real alternative that normal people could and did choose in numbers that Sony and MS couldn't ignore, pretty quickly.
Everyone switched from Palm to Android pretty quickly.
Google has a few extra levers which is agreements with all the phone manufacturers who in turn have to deal with the carriers, and google are doing the bulk of the ongoing os developement and security work so the manufacturers don't have to.
But they could just start doing that same work, or spin up a new 3rd party who's work they all share, easily, any time. They all actually already maintain half-assed backup plans they can switch to and go whole-assed if google gets that 1% too annoying one day.
There are really no easy robust moats any more. Even the biggest are precarious and have to be actively maintained through constant shenanigans. No matter how big the capture, it's never actually very strong.