Some misunderstandings on your review...
The K2 workflow is almost identical to the core Joomla! article system. Of course, it does not mess up with existing Joomla! articles (and that's the point in the first place). So if something happened to your Joomla! articles, that's your fault. K2 can only import Joomla! articles, it cannot write back to them.
K2 is of course actively developed. Don't forget it powers some of the biggest Joomla! sites worldwide.