This seems like a misunderstanding of the FreeBSD development model. Yes, immature code landed in HEAD, but it was removed before the next release.
In general in FreeBSD there's no expectation that HEAD is always usable. Sometimes it won't even build! It's a place where code can land in the hope that it will be ready by the time the next release rolls around, but "remove code which isn't ready for prime time" isn't an exceptional case.
FreeBSD has a very strong history of post-commit code review, largely because every FreeBSD committer gets email when commits go into the tree -- that's a lot of eyeballs. We're moving towards increased pre-commit review thanks now that better tools are available for that, but that's a separate matter.
(Yes, Netflix runs FreeBSD HEAD. I think they're nuts.)