Hm. Gentoo does have a developer's manual[1] which describes in detail how one would be able to package new applications or patch things in the main repository.
Working with Gentoo as a user does require having an understanding of the knobs that portage (the package manager) presents, and this has a certain learning curve. But that learning curve is IMHO worth it for the flexibility that portage brings to the table. Without that flexibility it would be very hard to manage replacing at user's will something as major in the system as the init system, or the whole audio stack or libssl provider.
[1]: https://devmanual.gentoo.org/
