Someone made a post last week about passive only working if you are in that stance (the comment was about using free stance to use moves from all trees but only if you switch to the tree, you can get the passives in that tree). This is 100% false. Easy test I did, I bought the HP passive for Healer (was in healer stance); HP increased. Switched to all of the other stances one by one; HP stayed increased. This means regardless of stance, all passives are gained and the best attacking chocobo for example is not by going pure Attacker stance, but by getting the str and crit rate boosts from the other trees.