The number of Android phone models where one can unlock the bootloader and install a custom ROM is fairly small. And among those models, there are plenty where no up-to-date custom ROM is available any more, so security vulnerabilities are piling up.

> you can still install non authorized apps on your Android, root your device, and install a custom ROM

No, you can't. Your device will fail hardware attestation because you "tampered" with it. Then everyone starts refusing you service based on that alone. Your bank app stops working. Your streaming app stops working. Your games stop working. No doubt one day WhatsApp will stop working as well and at that point my phone might as well be a paperweight.

I'm currently running lineageos with microg on a recent model phone, and google wallet is the only thing I've encountered that has given me any grief. Games, streaming apps, banking apps all work just fine. No hoops to jump through or anything.