I believe epidemic in raids needs to be nerfed. In certain encounters such VG, Sabetha, Desmina, Dhuum CM it just does too much dmg for too low effort. When timed right you can even work around the invulnerability phases of bosses.
I suggest capping the amount of stacks of condis you can transfer. 20 stacks of random condis (in total) instead of 25 stacks of each condition would be appropriate for this skill. That way VG wouldnt loose like 7% of his health bar instantly after being vulnerable again.