incredible flexibility in package versions. I can install multiple versions of a package, or install an old version of a package without incompatibility issues
can mix between rolling release (arch-like) and fixed / stable releases (fedora-like) on the individual package level
can very easily create packages not in the repos and treat them as first class
super easy to add and manage patches
global management of compile flags and options
packages in portage are not only programs. You can let portage manage other things, such as users or configurations
support for less common architectures or setups, like using musl, arm, clang, etc.
I love gentoo, but for different reasons:
Very true, what OP said barely matters nowadays but the features you listed definitely give Gentoo an edge over most other distros.
Also, we gotta shout out the sheer stability of gentoo and honestly having to compile system packages isnt that bad if you use flatpak.