I though "wisdom" (unless it's just opinion) is more in than out.
Yes you can only put as much in as you get out, but the "extra" flow not provided by the fans be that in or out comes through all the holes in the case (empty bays, screw holes etc). These holes dont havd filters, so more in than out (by fans) means air is leaving by these holes (positive case pressure) where as more out than on means direct is pulled into the case through these holes...and with it comes dust.
While cooling is the primary objective, if you get enough cooling either way then more in than out I'd preferable to help prevent that dust intake.
Some of what you are saying is true.
I'll try to explain how case airflow works by explaining airflow in general.
First things first.
Air flow is like water flow .. the science of airflow is 'fluid dynamics'. Airflow is like water flow.
Simple science says we cannot push more into a box than is flowing out out of box (case).
There is no 'extra airflow' 'in to' or 'out of' our cases .. same amount that flows is also flowing out.
For all intent and purpose, the only airflow we have in our cases is what fans are creating.
A case is not tall enough to create a chimney effect and flow enough air to make any difference .. and that is only if there are no fans in system moving air.
Case fans generate very little pressure. Less pressure than the pressure differential between dippping your toes into ocean and standing on a dock 8' above surface of ocean.
So yes, if we have 'negative' a litle air leaks in bringing dust with it, and if we have 'positive' case pressure then air will flow out those same holes in the case. But there is so little 'positive pressure' differential between inside of case and room, any air fans are pushing into case needs very low resistance areas (like vents) for most of that air to get out.
Hope that helps.