All the major distros, especially server distros, run systemd. That is proof enough that NOT running systemd is a niche and unsupported configuration in any half-serious setup.
A conjecture is not automatically wrong. The point of a conjecture is to challenge someone else to prove it wrong. You'd have a hard time showing proof that systemd is niche.
And honestly, it does not break UNIX, let's be serious now. A haphazard bunch of shell scripts is not much better than a monolithic binary, and UNIX does not give a damn either way.
I do not care about dogma and philosophy, I am an engineer with software to run and deadlines to meet.