Honestly, I don't see why people would have issue with BLM>SAM in optimal setting. Because in truth, optimal situation will be very rare. There are very few attempts where nothing will affect your BLM. I can't think of many time I did Lakshmi or susano where I havnt been targeted by a single flower, lightning rock or dice. if such a thing were to happen, I don't think it would be too far fetched to have the BLM>SAM . but since these situation are as rare as a 8 planets alignment, having the BLM DPS slightly above the SAM to ensure they are roughly equal due to the BLM loosing DPS during mechanics would be ideal.
I mean, SAM bring the slashing debuff, what does BLM bring? I give mana to a healer during transition. That's about it.