For a technical person, you have another choice: LineageOS (optionally with microG, which is what I use). It's nearly-stock Android without the Google apps, and with a few extra features. (Privacy Guard is very nice.)
microG lets you use apps that depend on Play Services without actually having Play Services - it's not complete but most of the common APIs are there.
There are other ROMs, but LineageOS (formerly CyanogenMod) is the only one I personally have experience with.
I love LineageOS, but using it still doesn't prevent OS-level privacy/attack vectors like the recent "report cell tower location despite location services being off" mishap/invasion. (1)
Yes, Android is open source, but at the end of the day Google is the dominant contributor, so you're still subject to their will... (just like Chromium)
Just curious how is performance and how old is the phone you are using with it? My biggest issue with android phones, even the google flagship ones is they just fall apart after 18 months both physically and with software overwhelming them to the point of extreme lags in every interaction with the device.
Does the same dividend exist here as on desktop where it’s pretty expected to be able to run a 10 year old pc by running Linux on it without much issue?
I personally use Lineage on a Samsung Galaxy S5 and love it. It's far better than the stock roms. It offers access to newer OS versions (currently Nougat) and quicker access to security patches. Better battery life, a cleaner less bloated experience, and options for tweaking settings to your liking. There are some downsides though. Mainly reduced camera performance.
It runs great on older phones. I have a 3 year old Moto G with 1GiB RAM. It will never be a speed demon but LineageOS Nougat is much better than stock Lollipop for performance on resource constrained phones.
microG lets you use apps that depend on Play Services without actually having Play Services - it's not complete but most of the common APIs are there.
There are other ROMs, but LineageOS (formerly CyanogenMod) is the only one I personally have experience with.