I've no idea what "Hide topic" and "Delete topic" are supposed to do differently. Both seems to be doing the same thing except that the name is different. Please make it more clear what these two features are supposed to do.
I tried looking for documentation but it looks like there is no documentation for Flow either. Perhaps it's time to write a comprehensive user documentation too (or if there is one, make it more discoverable)?
Components of the discussion system: "Hide", "Delete" and "Suppress" - analogous to revert, revision-deletion and oversight [...]" - so I understand "hide" as "revert", "delete" as "delete" and "suppress" as "oversight". It's about levels of access to the manipulated content (everyone/admins/OS).
It'd say it's an ontological problem, whether we should design Flow as understandable for all users (user-friendly UI) or mainly for those who have got used to wiki-slang (consistent UI).