I think you nailed it. Not being able to pass a cleaner, and even the gurgling itself, is a symptom, not the problem. The problem is a poorly executed airway. Some pipes are inclined to poor airways because of severe bends, but still some makers are able to execute a very good airway in these challenging shapes so I'm inclined to believe that the ones that do show symptoms suffer from a lack of concern to get it right.
I find just as much trouble with constricted bends in the stem and a narrowing airway in the stem as I do an issue in the tenon area.
These are horrible times and all sorts of horrible people are prospering, but we must never let this disturb our equanimity or deflect us from our sacred duty to annoy and hinder them at every turn.