Both runit and s6 are copies of daemontools which hasn't been updated since 2001. Try doing diffs of runit and s6 against daemontools. Are the differences are significant. What "improvements" were made.

Things can be built to last, including software. That so many programmers today are not building such things (possibly they are incapabale) does not change fact that some did so in the past (whether intionally or not), and some still can.