As someone whose nearest exposure to a "source based distro" is FreeBSD, this sounds like madness, as it means a broken build could not only impair attempts to repair the build, but render the system unbootable and/or unusable.

And as someone who regularly uses traditional Linux distros like Debian and Fedora, the idea that a package management system would allow a set of packages known to be incompatible with one another to be installed without force, or that core package maintainers would knowingly specify incorrect requirements, is terrifying.

While I'm not familiar with Gentoo, my reading of this article suggests that its maintainers are well aware of these sorts of problems and that Gentoo does not, in fact, suffer from them (intentionally; inevitably mistakes happen just as they occasionally do on the bleeding edge of FreeBSD and other Linux distros).