Also I've never seen a Kanban operation deliver everything to Production as soon as it hits a "Done" column and there's no reason not to "time gate" (once every fortnite, just like Sprints are supposed to be, for instance) a Production column "pull".

I think that's easily missed in Kanban versus Scrum discussions: every Kanban column is supposed to be "pull" rather than "push". Production "pulls" finished UAT stories when it is ready (which maybe is a biweekly schedule that keeps ops happy and gives marketing time to prepare materials, etc). (I also think that's why a lot of micro-managers dislike Kanban versus Scrum, because they want to "push" everything and dislike people making their own "pull" judgments based on their current bandwidth and ability.) The failure case of "Production pulls finished work" is that Production sometimes wants to cherry-pick finished work ("I want these three but not this fourth one") after they've been already merged for UAT testing. I've not seen a good Kanban software that visualizes that "state change" of stacking cards together as they become bundled together/releasable units.