There is a lot systemd violates in regards to the traditional Unix philosphy rules. The one about do one thing well is probably the most arguable though since systemd is more a set of functionality across a ton of binaries, each with a more focused purpose. Where it differs is in how those interact vs a "normal" collection of Linux binaries where it's expected to be easy to swap out an individual component and still talk to the rest without implementing things like binary formats.