That has never been true, not at the point of the discussions on Debian (on Arch there was never a public discussion that I remember), and of of course not true now.
s6, dinit, runit, openrc and shephered are good options, currently in use by different distros. At the time of the public debian descussions, at least runit and openrc were available, but they were dismissed, and I don’t remember the arguments, but not so convincing at the time, thus the whole discussion about the topic.
I’m not a systemd opponent, but claims of not having compelling alternatives doesn’t feel right. I used Arch with systemd for a while, and I moved later to Artix with s6, and I’m thinking on testing dinit, and I have no issue. I guess if some major distros had made the move to runit or openrc, they would be more used as of now. BTW, at work, for containers and VMs I actually need to use systemd, and I see no problem with that.
It’s totally true sysVinit was way hard to keep maintaining on distros, and something else was required. Probably given the influence from major distros changed the game over systemd, and now that’s considered standardization now a days, but something else could also have become the standard. What’s for sure is that there are success stories of using something else, Guix with shepherd, Artix with several inits (dinit, s6, runit, openrc), Gentoo with openrc (one can choose others, like systemd), void with runit, chimera with dinit, and the list goes on. Variety is not necessarily a luxury, in this case it means one can choose whatever aligns better to one’s needs, believes (perhaps simplicity, perhaps minimalism, perhaps free/libre considerations, etc), and so on.
What’s also true is that for work purposes, one can’t be negligent learning about systemd, most probably one will need to deal with it sooner or later, because major distros, and in particular commercial ones, already embraced systemd, and that’s not changing any time soon.
The sad effect of wide adoption of systemd, whether one opposes it or not, is that now services/daemons developers focus on providing systemd ready daemons, and for anything else the distro developers need to port to non systemd alternatives, and even build applications without systemd if that’s possible at all. And if one is looking for a daemon not packaged by the non systemd distro of choice, ones is on our own creating the proper service/daemon, but not something impossible.