I understand the difference between the ACs, I leveled a Merc to 30 and a PT to 50. But you didn't say the Merc would out dps the PT, you said the PT was not viable.
PTs have a good output if spec'd and modded well. Also a Merc has the potential to be lower on movement fights due to high damage attacks needing a cast time. The PTs only one is flame thrower. I admit I've done no number crunching as of yet, but to say the PT is not viable is silly imo. It may not reach the potential of a Merc, but that doesn't mean all that much.