> 5) Patches frequently are FreeBSD specific so can't be committed as-is by 
> upstream official developers.
Much better than nothing. I always get patches from Debian where they
are often specific to Linux.

> 6) Patches seem to rarely be submitted upstream. A FreeBSD port may have 
> fixed a generic problem years ago but appear to never adequately share 
> their fix. (I have seen this several times over several years.)
The same to pkgsrc. I'm upstream maintainer ;) Most bug reports and
suggestions was obtained from Debian people, some from OpenBSD,
nothing from pkgsrc.  If somebody from pkgsrc people invite upstream
maintainers to builk builds mailing list, things will probably change
soon. ;) Pkgsrc has a uniq position, it has access so many hardware
platforms and operating systems... IMHO bulk builds from different
computing environment is one of the strongest side of pkgsrc, at least
for developers interesting in developing a portable software.
Unfortunately only two systems use pkgsrc as an official
packaging system. As a result support for Linux, FreeBSD and others
are much worse than for NetBSD and DragonFlyBSD.

-- 
Best regards, Aleksey Cheusov.