Mountain out of a mole hill.
Lack of debuggability? It's not like this is some threaded golang program you'll lose your mind attempting to make sense of in strace. systemd is a single-threaded C program, if you consider this as not debuggable it's your failing not systemd's.
There are valid complaints to be made about systemd, but from what I've seen the crux of the problem is generally the haste with which its features are conceived and developed. For the most part it's a relatively conservative codebase, in a simple and easy to understand language without much of a runtime interfering with relating the code to the underlying system calls performed.
This project doesn't have very many core contributors. It's somewhat incredible how much has been achieved with so little. But as a result, it's not perfect.