In FreeBSD at least there is a real, fully-featured, usable OS out of the box, all consistent, in one source tree at /usr/src which is quite easy to read, change, and build. Unlike most GNU/Linux distros where each random thing like "grep" is its own package developed by its own separate group of people.
Linux distros avoid this problem by separating the process of committing to an individual port/source package; building that individual package, and possibly rebuilding dependencies; and pushing out updates, which are atomic and can contain an updated library and all of its dependencies. My experience is that Linux package managers (dnf/rpm anyway) are better at catching operations that would introduce broken ABIs, as well.
In contrast, the FreeBSD ports model is to invoke poudriere periodically and rebuild all ports at once, then push the entire set out to mirrors. There is no automation that checks for ABI changes in libraries, and pkg(1) does not do a great job of confirming that a library upgrade does not break installed programs (or other libraries) via SONAME bump; much less symbol changes not reflected in SONAME.
rm -Rf /var/db/pkg/* /usr/local/* /usr/ports/distfiles/*
reboot the system and all the non OS packages (installed via ports and packages) are gone and you can start over (reboot is probably optional).
This is true for the base system, but not necessarily true for ports / pkg. You can end up with an inconsistent pkg collection, unfortunately.