PvP Materia = Useless

[Djlovedrop]

Miasma applies heavy plus another dot for the damage + healing reduction. The damage and healing reduction isnt reduced but the heavy is. I just tested it.

[TaneshimaPopura]

Healing reduction is combined with the Disease debuff. Miasma applies the Miasma debuff and a Disease debuff, If as you claimed that healing reduction time isn't reduced so is the 50% slow from Miasma. And besides highest Heavy is only 40% where BLMs get a 20% version one.

[Sunako]

BLMs get both 40% and 20% but u need cast blizzard for the 40% ones and the 20% one also reduce casting speed too