> On the other side, you have a monolith that hit 1.3 million lines of code a few years ago, and has gotten more and more complicated since then.

Just a nit, that 1.3 million lines was reported incorrectly. You can see some talk at https://news.ycombinator.com/item?id=21935186 and I remember a Poettering tweet saying that was including things like documentation. At the time systemd was under 500k lines; still big but not quite so huge.

I'm also not sure if that count was for the full repository (which contains multiple modular projects like systemd-resolved that are not required for systemd) or just the actual systemd bin.