You do have the option though. I run LMDE7, and installed a 7.0-prempt kernel yesterday because I felt that I was seeing too much stuttering in 3d games. I installed it from my package manager which already had debian Backports turned on.
Amazon’s Fire OS is android but they’ve announced a new webOS ripoff, VegaOS, Linux running HTML5/react apps. Normally I’d think this kind of diversity is a good thing, but apparently it’s locked down even tighter and side loading into Vega OS just isn’t a thing at all.
Edit: the point I was trying to make is that some vendors are working to get away from Google’s Android foundations completely. I would think that graphene could go that route if the rug was pulled. But good luck with device support when the device specific source isn’t released.
I recently went about setting up an account with an email provider that purely provides mail. Very happy with them so far, the only thing they don’t do that I do use with my free legacy gapps is Google Drive.