The really early adopters seems to have been offshots of Fedora. And i do wonder if Debian was a holdout until systemd started sprouting containerization features, and Canonical (Ubuntu) was feeling the heat.
The whole systemd vs sysv back and forth is a smokescreen, because while sysv stops at init systemd continues on to cron, networking, sessions, dhcp, dns, /dev, and soon to be ttys etc.
And while the kernel is maintained under the rule that change do not break user space, systemd developers seem to do changes with a permanent "deal with it" meme.
LOL no. distro maintainers wanted to ship gnome, which was product tied to systemd. No systemd, no gnome, that simple.
For what is worth, all the Debian maintainers I know, even those who are not systemd supporters, felt that sysvinit had to go in a way or the other (eg. during the default init debate the options were systemd and Upstart, sysvint was doomed to be replaced and only kept as a compatibility option in any case.)
https://bugs.debian.org/cgi-bin/bugreport.cgi?msg=1729;bug=7...
https://bbs.archlinux.org/viewtopic.php?pid=1149530#p1149530