Actively Discouraging use
Google actually intending for the takeout archive to be useless would certainly explain the data quality I experienced while trawling through it in order to re-publish my content.
This is not a statement by Google itself, but then Google has been pretty phenomenally silent about the whole Google+ shutdown thing. By letting this moderator comment stand without correction in the official Google+ help channel Google is at least silently endorsing this actively hostile position.
Update: Google quietly improved Google+ Takeout archives a few months after announcing that Google+ would close. I didn’t get to benefit from it because I had already done my export.