If you want a compromise, like me, Cyanogen with out GApps. What other options do you have?
The more I got into Android, the sooner I realized it was a crap shoot when addressing your question and my core interests in hobbyist computing on phones just like computers.
Play store alone has enough permissions to collect call metadata
So even if you find a relatively safe Android version to use, you're getting a heavily gimped experience where a very limited selection of apps work. (Generally, what you find on F-Droid.)
I guess the question is how you define a platform or an operating system, but I think that the platform apps on it run off of is a major part of it. And the difference in what will run on AOSP and what will run on Google Play flavored Android is staggering.
And even though it uses Linux as kernel, even that doesn't matter.
The API surface that NDK code is allowed to use is so constrained that they could replace the kernel with something else and only OEMs would notice.
Google could be more open. But there isn't any evidence the parts of Android that are not open are not open in order to stop open or even competitive semi-closed Android derivatives.
They are open enough enable competitors to use the same technology platform, including some very valuable technologies like the ART compilers. If they intended to lock out competitors, they could easily have done so.
Samsung can't compete because there is no viable Samsung ecosystem, and Samsung has not aligned with an ecosystem partner other than Google.
The problem is that Google is creating a walled garden, to prevent competing app stores. Apps developed on Android could be easily listed, downloaded, and installed on any flavor of Android. Samsung, Amazon, etc. could all have their app stores, and developers could script a simple command to update their apps everywhere.
However, by creating a proprietary layer like Play Services, Google has effectively made a proprietary fork of Android the dominant one, requiring different levels of effort to support non-Google phones.
You could try this: http://opengapps.org/
If I correctly understand `Last modified: June 28, 2016, they are writing`, this feature should not be available before that date, so either it comes as an update to a gapps or to Android.