My personal definition of full blown OS is something that considers me enough of an adult that it allows a file explorer / remote shell based file sync rather than use of a specific sync app or MTP.

Sad thing being that Android had that, and then it was taken away (my personal suspicion there is that it was done as part of an agreement with big media about content in the Play store).

Not really? I'm not sure what would be ambiguous about it.

For one thing, Android is based on the Linux kernel. The very same kernel that is driving the majority of servers on the net right now.

An OS is more than the kernel.

Android/Linux is a complete different animal than GNU/Linux.

Can you really say that when you can install a terminal, get shell access, and drop in a Debian based chroot?

Yes, because it isn't any longer Android.

I guess:

- it isn't running the standard kernel, which is not 100% like a vanilla Linux

- it is making use of non official NDK libraries

- doesn't make use of Android user space, which given the NDK limitations is like 90% Java

It is just like putting Wine and calling it a Windows distribution.