If the issue is a single module take over of userspace then I have good news for you. The systemd project is made up of multiple modules handling differing tasks not all of which you have to use.
Every time that this argument comes up, people don't get their computer science right. The problem is not whether something has modules. It is the degree of coupling amongst and cohesion within said modules that is the metric.
There is significant variety between distributions regarding which systemd project modules are used by default. Many distributions also allow systemd modules used by default to be easily replaced with non-systemd alternatives. This speaks to the level of coupling and cohesion between systemd modules being low enough that they don't form a monolith.
Waving around the terms without understanding them, as you are doing, demonstrates exactly what I mentioned. Someone who actually knew the computer science would not be talking of low cohesion here, or of modules forming a monolith.
Modules which only work with their own other modules and fail to work with other people's modules aren't modules, they're a monolith.
with accessories.
Would you say Postfix is a monolith? Or qmail?
yes and yes. Fairly small ones, but monoliths nonetheless.