Can Galaxy even run without Linux kernel?
In theory yes. Android doesn't expose a proper Linux to userspace and Google has been clapping down what we are allowed to do with the NDK since Android 7.0 (edit: corrected, only started in 7.0). So playing "what if", you can replace Linux with something else that is compatible the NDK APIs and no one would notice, other than the OEMs.
Makes sense. That way there isn't a massive stockpile of old useless Android devices when the "new Google OS" comes out.