It is basically about small tools, limited in scope, that solve a problem surgically and comprehensively. They work together by mixing and matching to solve the problem.
systemd is sort of like if microsoft word took on system init. In the beginning it was small, but now it is web based and does videoconferencing.
I don't know, it is sort of like busybox, replacing other system components in a limited Minimum Viable Product way, but more like limited function, not limited resources.