I think BLM makes the better healer guard because between Heavy, Bind, Sleep, Virus, Eye for an Eye, Lethargy, BLM has far more options compared to PLD's gimped stun and Cover. With how many SMNs and BLMs running free due to lack of focus in mass encounters Cover won't stop that magic damage from killing off your healers. MRD/WARs are probably better than PLDs though for rushing backlines though because they can get in, berserk, burst someone really fast and get one and BRD is pretty hilarious for healer harassment. I was in voip with a bard friend of mine and we would buff to max for barrage and focus a healer at the same time and it's crazy how fast they burn. I'm sure they had no clue what was hitting them because BRD animations are so ignorable.