Something is definitely wrong with pyro merc damage. I have full BM gear and put all my original mods back into my gear for the expertise buff. i have close to 1200 expertise now and none of my abilities hit nearly as hard. Before, a thermal detonator could hit a guy for 3500-4000, now im lucky to get 2000-2500. Pretty much the same proportions for Rail Shot and Rapid Shots.
For a guy who normally did 400-500k damage per match on average going to about 150-250K in a full match. I can tell you something is definitely off.
What's even more troubling is some mercs claim their damage went up. This seems logical since the new expertise gap should theoretically see a damage increase. The fact that mine went so significantly down without really changing any play style is very disturbing.
I hope this is some sort of bug that will be fixed soon. I have no idea what is going on.