hideIfEndpointEmpty does not hide Workflow State presentation
One answer
I don't think this was ever meant to be used for the state, however, since it is available, you should consider to file a defect or a PMR.
As a user, I would hate this kind of implementation. A better, but more expensive solution would be to write an advisor that prevents saving of the work item if there is no defect linked to it and provides a clear message also. See https://jazz.net/forum/questions/105644/can-not-change-contributor-list-type-and-duration-type-to-readonly/105789 for a similar question and some hints on how to proceed.
Comments
Adding an advisor may be a more elegant solution, but it has a couple of problems. I find it very annoying in RTC to update a work item only to get an error message when I try to save that I did it wrong. If I can be prevented from doing it in the first place that is preferable. Also, modifying the editor presentation is less invasive, so it presents fewer problems with new versions and other changes. To complete my description, I planned to present a message if there was no link selected. The message would be replaced by the workflow state when the link is selected.
Interesting that the thread referenced above includes an additional comment that contains a link, https://jazz.net/library/article/808/ , that proposes essentially the same solution I asked about.