Yes he did the opener with B4 but as I already said B4 ahs only a value when you CAN cast those 6 fire IV and that is not always possible, we haven't seen yoshida playing around a real raid scenario (btw we know he tests them with his BLM) so it's possible that we want to use them in specific situation, also remember that yoshida acknowledges the fact that the community can find more effective ways to play than them