Up to me the problem with counterbalace was the difference between 4vs4 and Frontline.
SMN are one of the best class with a low amount of people or probably the best one for 1vs1 even as caster, so they nerfed him for 4vs4 adjusting miasma, but I think it was due cause of Miasma II, that could slower an entire party, and in pvp it is obviously over powered, but I think that they should leave the full Disease effect to Miasma.

By the way SMN are not a bad class, you don't kill with your DoTs, but bursting your enemy with Fester + Energy drain + ruin II and even PvP skill Pet all together, or atlest this is how I get kills :/