I hear you. I re-read the rules to understand how and when the fall condition starts and then why and when the fall condition damage is applied. A dexterity save is rolled to stop the character from losing his/her balance, and therefore catch himself/herself before falling. Once the character is falling, unless by some influence: class feature, spell, or item, normal fall damage applies. The barbarian rage stress-tests the rule because unlike the monk's slow fall which is applied to the fall condition, the barbarian's class feature mediates the condition under a specific circumstance: rage. To make use of the damage resistance to B, P, S damage, the barbarian must be raging through the initiative count and until the fall ends.

As far as rate of descent, I home-brew the climb rule into the distance fell rate. It's the easiest to transfer and it's already built into the system. A character can climb half his/her movement per round, which also conveniently provides spell casters a mechanic they can rely on to help the barbarian slow his rate or fly back up or some other clever use of a spell book.