My main is a powertech. While I spent most of mine time spec'ed as a shieldtech, I did play around with pyro and AP. I personally found the DPS trees under powertech to be awesome PvP specs... Not as outstanding (though viable) PvE specs. I can't tell you the last PvE group I've been in that had a pyro or AP in it. For PvE most people seem to gravitate towards mercs.
As a tank and guild officer I can tell you mercs are great to have while running end-game HMs and ops. Not only can they lay on massive damage, they can also pocket heal. It's a very versatile class for PvE.
Gotta disagree here on the part where you said they are not "outstanding" PVE specs.
I have a campaign/black hole level Pyrotech DPS, and I pretty much only raid with him. The damage output is incredible, and while it is feast or famine with your railshot proc's, you can still more than hold your own. Whenever an enemy is being DPS'd too much, it's either myself or our guild Mara who is called to switch targets (Zorn/Toth, Jarg/Sorno) or back off.
Remember, Thermal Sensor Overrides are your friend for using Incendiary Missile
Here is my opening rotation, by the way: TSO for free Incendiary Missile > Explosive Fuel > Rail Shot > TD > Flame Burst > PROC rail shot, if not, Rocket Punch > PROC railshot, if not flame burst> Explosive Dart > Unload > Rocket Punch etc etc etc
Heat management can get me from time to time, but I am very rarely in an "oh crap, too much heat!!!" moment.