As an ex-Gentoo user I can confirm that compiling speed still matters on certain machines.
I have never worked as a system programmer so I never had the need to compile something big. I guess it could be an issue with very large software like Oracle Database, the Linux kernel and other similar stuffs.
The kernel is quite okay. On the other hand, qtwebengine..
Well given that often the alternative was BASIC which was interpreted, it also felt fast to run..