Well, if you will dig into the guts, you will find some 'suspicious' files, but those are emulators so apps that depend on systemd works without complaining. But yes, OS runs without systemd. Linux MX is being described as middle weight system. But I heard some were installing it on older systems and I decided to try it also, and my experience is, it actually goes to light weight category, I was really surprised. Probably lack of systemd helps too.

But if you have happen to run into too old computer then there is always Antix available, which is definitely lighter. (MX and Antix are cooperating, sharing code, and both are without systemd)