Definitely not Gentoo based, but if you can get by with their unique approach to basically everything, NixOS can be pretty interesting, in that while it is technically source based, binary caches are widely used to basically “pretend” to be a binary distro. And it does let you patch things shouid you want it (at the expense of recompiling everything that even slightly comes in contact with the patched package)
There are some parts that are too “baked in” to change – requiring systemd, for instance – so that may be a dealbreaker for you.