Unix philosophy has a reason. It allows to easily replace components and simplifies testing. AFAIK it's not easy to replace various parts of systemd, it's very monolithic and it does too many things.
You can easily replace timesyncd with any NTP daemon. You can easily replace networkd with any other networking manager. You can easily replace timer units with cron. You can easily forward log messages to a syslog daemon. You can easily replace systemd-boot with grub or any other boot manager.
It should be pretty obvious how baseless the monolithic arguments against systemd are.
(And was just wondering if there was any specific thing the original parent wanted to replace.)
Again, was just interested if you had any specific thing you could point to, but elsewhere in the comments I see now a few concrete issues.