Wind > Fire > Ice > Wind and Earth > Thunder > Water > Earth is actually supported by in-game manuals. I'm fairly certain the swimsuit water affinity boost and water damage cut is just a nod to the fact that swimsuits are for use in water and not really to be taken seriously >.>

If there was any sort of "Defensive" element chart it would be mentioned in game and it would make things overly confusing anyway. Boosting your wind affinity makes you stronger both offensively (element-wise) and defensively to fire, its just that the stats aren't working correctly.