Powertechs are slightly superior based on talent tree. They get 90% armor pen railshot chance whereas mercs get 9% aim(which scales) if both are specced X/X/31. Powertechs get 3 interrupts(long range grapple, quell and carbonite) and a 25% crit chance every 2mins. Pyros need to have combustion on to kite melee and therefore mercs lose out on 35% armor pen cylinder. I play a Powertech but i have always been intrigue by this Merc pyro combo setup. Like AP/PoM Mage, the only issue is heat and its role as inhibitor. Relic or Adrenal->Thermal Det(16) -> Incind Missles(25) ->Power Shot(25) -> Railshot(8) -> Power Surge -> Power Shot(25)+. Pray for railshot RNG on both Powershots. That leaves you way too overheated. Vent Heat at 90secs CD would probably help though.