That's the point. Gentoo isnt one of those. You can use it with systemd, it's supported.

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.