I have found that during Prime Timein PvP, it is definately. Skills do not work, there are desyncs and lag. But when its off peak, my skills work 99% of the time and the combat its ok.
This! I literally was just in a 2 man group during off peak hours in the main locked campaign, and it was fine until it got later throught out the day and it was hot garbage and this was in ALL campaigns including the sewers!