I agree, I think thirds is not conservative enough at all, even in high flow caves. I think if a real OOA or other very serious emergency happens having counting on the flow to make the exit faster and thus reserving less gas due to that "help" is being unrealistic and overly optimistic about how stuff will most probably go in a real situation.

In no flow caves thirds is definitely not enough and I do not understand why it is an accepted and taught safety margin, I think you can never go wrong with having too much air, but you can very easily go very wrong with having exactly enough.