No. You are ignoring the damage from CGC, which is almost 2x your 800 damage differential AND is elemental just like FB. So net, FB is going to more damage than PS, even if the target has zero armor. Once you factor in the target's armor, FB doing 50-100% more damage than PS is common.
cgc is 100% of the time on the powertech's target.
and flame burst will be used far more frequently then it would be needed to just refresh the cgc. (don't forget that you only have 4.5 sec until you can proc 'ppa' again and you will use fb multiple times in a row until you get it) cgc is also refreshed with each railshot ( which should idealy come every 6sec) and each basic attack has 3 times a 16% chance to trigger it aswell. so of around 4 flamebursts only 1 recieves the bonus you are speaking of.
and yes i agree, dps mercs do currently have no place in ranked wzs.