I'd have to test it out, or someone else can, but I'm not sure that is entirely accurate. Buffs tend to come form our side, the caster, which is why they aren't effected, but debuffs tend to be placed on the other side, the receivers. There aren't many debuffs that lower the healing given, I only know of the one in Hullbreaker HM, but most debuffs lower the healing received, disease being the most known.
