The Bards buff was for PvE and not PvP, I think they might,ve just forgot about PvP when they decided to buff bard. Still considering MCH ability to burst even if Bard still got a pretty good burst combo (Barrage empy + Sidewinder + Farshot + Bloodletter + Misery end), MCH was still able to pull a pretty huge burst himself, in the end I guess that 4,5% buff on his burst (Empy + Sidewinder) will probably get them on par.
The problem might come from the blunt arrow, that +60 potency is going to be really good in PvE but might become a bit strong in PvP.