You didn't read correctly.
I think we're talking past one another. I'll try to be clearer.
I said, that if you think Play is keeping you safe, nobody prevents you from only using *Play*.
Sure, but that's not the point. The point is that Android does prevent most users from using anything other than Play. Not by actually blocking them from using other app stores but by simply not offering the option. And that's a good thing, because most users have no idea how to decide whether or not something is safe.
I think perhaps the confusion here is because you and I are looking at this from different directions. You seem to be looking at it from the perspective of what you or I might want to choose. I'm looking at it from the perspective of an engineer whose job is to keep 3B users safe, most of whom have no idea how to make judgments about what is safe and what isn't. Keeping them within the fenced garden (it's a low fence, but still a fence) allows them to do what they want without taking much risk. The fact that the fence is easily stepped over preserves the freedom of more clueful and/or adventurous users to take greater risks. I think this has been a good balance.
And while you are usually (not sure for all manufacturers) not prevented from using other stores
I'm pretty sure that the ability to allow unknown sources is required by the Android compliance definition document, and that a manufacturer who disables it is not allowed to call their device Android, or to pre-install the Google apps or Play.
Google does a few things to make it uncomfortable. Trusting the store is a one-time thing, but you still have to acknowledge every app install twice and updates require confirming you really want to update the app, while Play can update apps in the background, optionally without even notifying you.
Until Epic decides that they want their store to be able to install and update as seamlessly as Play can, and gets a court to order that. Still, your point is valid, there is still some friction for other stores. Is it enough? I guess we'll find out. Will it be allowed to remain? I guess we'll find that out, too.