This exploit isn't in PID 1 and neither are all of the other things people claim are in PID1. PID1 in systemd doesn't contain much more than it needs to, it handles parsing unit files which could arguably be split out but that still leaves something highly privileged to parse them, but just about everything else would be a major pain to separate from PID 1 as most of it is how to walk the dependency graph from where it currently is to the target that it's trying to get to. It also needs to handle supervision and other core parts of init but by and large most of the claims out there that everything and the kitchen sink is being put into PID 1 are completely baseless.