I think this is a really old statement. I’ve used systemd since it was made default in Fedora back in 2011 (Lovelock, anyone?) - at what point am I qualified to have an opinion, after having used it personally for 13 years and professionally for 8.
systemd is scary for 3 reasons.
1. it is inscrutable. Debugging it is nearly impossible, so you had better hope you don’t get a buggy release, especially with how hostile the devs can be.
2. it is large, and growing. Lots of things it claims are optional are in reality: not really. This is fine until uou get something that really doesnt work well (systemd-resolved is consistently the largest reason I have connectivity issues, wether it be because it interferes with docker inter-container networking or because it needs to time-out when trying DNSSec to continue- or if it fights with my vpn provider for power over my resolvers etc). Due to my distro being very tied to it: I gotta keep using it and working around it.
3. The interface is irreplaceable. Why are their 13 init systems? Because init is a closed scope. To be a sucessful init you need to spawn processes and do it cheaply. Supervising processes after start? Noble, and there were implementations that could do that (CDDL licensed SMF from Solaris for example). However we have already reached the state where it will be literal man-decades of work to replace systemd as we will need to make any replacement bug compatible with systemd itself. Its the ultimate show stopper.
The implementation is the reference. Which is a large departure now from what came before.