That means the lack of huge software like Gnome

Been using Gentoo since Jan 2009 and one of the reasons I moved to it and never looked back was because it let me tailor "huge software" like KDE to my needs, with the aid of USE flags and sets. That's what an actual customizable distro let you to do. If you want to use "smaller software" like, say, Openbox, it won't get in your way either.

So that point of "centered around smaller software" strucks as weird to me - it goes against the "customizability" point and, ironically, the very Linux kernel is "huge software"...

If they get dinit i'll probably try it

sysV is the init system linux distributions used before systemd, openrc, upstart, runit, smf etc. It’s pretty much the old daddy and comes from Linux unix roots. Even MacOS used it before they made their own called launchd.

S6 sounds like a update to it since the capital V in sysv stands for the Roman numeral 5.

Source based distros are niche enthusiast things. I can't say much about them. I like the minimal and lightweight focus though. Also I prefer runit as an alternative to systemd.