> When Debian adopted systemd, after some debate, every Debian-based distro did too. This wasn't considered a particularly invasive change at the time. But systemd started to expand into its "middleware" position, absorbing vital system functions like udev.

Your timing is off. udev became part of systemd in 2012. The big Debian debate was in 2013-2014, and was acrimonious enough to eventually cause several of the CTTE members to resign their position over it. One of the core issues driving the Debian systemd debate was the fact that GNOME was planning on dropping support for anything other than systemd-logind (or something like that), and there was definite concern that packages were already making decisions that were forcing everyone to adopt systemd as the only init system.