There are many distributions without systemd. Voidlinux and slackware have rolling releases and are very clean, for example.
Slackware(1993!) has been around longer than Gentoo(2000), but USE flags, slots, _choice_ and control over the compilation stack are pretty nice. NixOS's package manager and portage hopefully merge sometime in the future. I havent tried Void.
We didnt need to have the init system debate, it was never a possibility that Gentoo would be monoinit.