Hi,
We advise people to treat the DB like a black box that you really want to keep your hands out of. (Obligatory Dune reference.)
Instead you should use Administration → Projects → Management to delete these project. You mentioned that “manual batch” deletion was tedious. Were you referring to this page? If so, you should be aware that you can script the calls that page makes.
The best way to master the API is to perform the desired action via the UI and eavesdrop to see which calls the UI made to accomplish the action.
You may also find this guide helpful.
Regarding the setting you found, its for deleting analyses, not projects. And it’s not going to kick in for dormant projects because housekeeping only kicked in during (at the end of) server-side analysis processing. (It’s possible that it needs to be a main branch analysis, but I’m fuzzy on that.)
HTH,
Ann