True, but Google's own implementation of Android in the Pixel does allow you to re sign the bootloader so you can install your own OS and securely boot to it. And "Android" isn't all the same. It's a broad and shared ecosystem.
Also, we have a gatekeeper called Google Play Services. In other words, even if you have a custom ROM, you need that all-encompassing framework to have nice things.
Clients may differ, but the cloud platform and the connector which enables all these "Android" things is closed source, and controlled by Google.
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If you want to install microG super easy and are still choosing your next phone, get one supported by LineageOS: https://wiki.lineageos.org/devices/
Then instead of the official LineageOS build, get one from here with microG preinstalled: https://download.lineage.microg.org/
For low budget folks, a lot of Xiaomi phones are supported. You'll have to sign up for their account and wait for a few days, but otherwise the process is pretty straightforward. E. g. this is for my current phone: https://wiki.lineageos.org/devices/ginkgo/install