Even if we can't define the "UNIX philosophy" exactly, I think we can still look at a given software system and see whether or not it generally approaches that

Even if we can't define the "UNIX philosophy" exactly, I think we can still look at a given software system and see whether or not it generally approaches that set of ideals as a whole. When compared to UNIX-oriented software of the past several decades, I think it's clear that modern GNOME is very different. Systemd is also very different. Being so different in so many core ways means that they inherently don't adhere to the practices and ideals we can consider to be typical of software adopting the "UNIX philosophy".