Gentoo, as a matter of fact, offers lots of freedom. Its package manager has built-in capability to distinguish licenses. You can choose between systemd or openrc. Musl or glibc. You can disable all sorts of configure options you don't want or need. You can use it stand-alone or inside another distro. You can specify cpu flags for the compiler globally and per package. You can drop in your own patches for any package (and yes, I use that too). You can more easily modify just about anything in the entire system than most distros.

Using Gentoo lets you build a useful system for whatever you do, from sources or binaries, tailored to your needs, without the burden of having to learn all of the different build systems, their dependencies, and weird quirks you'll come across as a package maintainer of any distro. Ever looked at the rpmspec of things you use? Or the patches in a Debian source package? Those details are all taken care of, but with portage still customizable on a high level.