I don't really agree with this take.

I do think that it should be easier for people to build and install alternative OSes on their phones.

However, building your own mobile OS is just really hard. And on top of the technical challenges, the UX challenges, the overall polish challenges, there are non-technical challenges that are often impossible for alternative OSes.

* Industry connections problems. As an example, no open source mobile OS has a contactless payments app, at least not one that is generic and can support more or less any credit card out there. That is, you can't build an Apple/Google Wallet analogue and have it work.

* As much as I wish Jobs had stuck to his guns on the "no iPhone SDK" thing, and had instead developed and improved the mobile web stack, that's not the reality today. There are many things you just cannot do current mobile OSes through its web browser. Native apps are required there. And so that means companies need to choose the platforms they build for. Today that's easy: iOS and Android. But getting governments and banks and various companies to build apps for your niche mobile OS is going to be essentially impossible. And with closed-source kitchen-sink libraries like Google Play Services, it's incredibly difficult even to get a lot of Android apps running properly (and consistently reliably) on "de-Googled" Android phones.

Ultimately the real problem is that there's no capable, standardized, OS-agnostic platform for building mobile apps. The web platform could have been it, but it's not, and now Apple and Google have a vested interest in ensuring that it never can be, because building native iOS and Android apps locks people and companies into those ecosystems.

Ultimately^2 the real problem is that free markets are a myth, and don't work. Companies want to become monopolies, and want to bar new entrants. I would absolutely love some mandate/legislation/whatever that made it mandatory that we have a fully open source mobile OS, and that all the players involved need to be allowed to build equivalent functionality into it that Android and iOS have. I know that sounds radical and like government overreach (and current governments wouldn't go for it anyway). But the alternative is what we have today: monopolists that don't care about the rights of their customers. There's really no "free-market" way out of this.