So they created eudev because it was becoming more and more of a hassle to dig udev out of systemd for use with non-systemd installs.
And i think LFS has also adopted eudev for their "traditional" book now, because they ran into the same issue.
Something like this should really give pause for thought in the "init" debates, as it is a stark reminder that systemd has gone far beyond being just about init. And thus all those videos demoing systemd vs "random init of the day" boot times end up being a distraction rather than enlightening.
Gentoo offers even more freedom of customization than Arch. Choose your init system, your udev variant, your main Python version, set around 100 build time options for ffmpeg and so on.
LFS is great for learning and looking under the hood, but for a system that you actually use daily, Gentoo has no rival.