What I think is that Purism got it wrong by creating its own mobile distro instead of starting from a pure-FOSS Android (AOSP) and patching the missing things with thinks like microG, better permission system, isolation and ways to force closed source apps to behave and obey the user (app wants my address book and refuse to work if I deny it? Nice, take this randomly generated list of names and numbers! Location? Take this random place. Phone or cell ids? Take this random stuff...)
Advantages is that they can start with a bunch of free apps (F-droid is nice!), do not get too far from what SoC vendors already have and can move to another distro (even running both them in parallel) once they sold a good number of devices and the business is sustainable. All while respecting user freedom even when they really need some proprietary stuff (e.g. bank apps).
But, well, that ship has sailed. Let's see what we can do.