Why the hell are PPCs useless pieces of junk?
Possibly because you're firing them from within 90 meters where the normal version has a (grossly underdocumented) minimum range and suffers from damage falloff within this range.
ERPPCs have no minimum along with their extended maximum.
They currently aren't being lag compensated in the way that lasers now are, so you might also be missing moving targets despite the fact that it looks like you're hitting on your screen.
Either way, a pair of them does the same damage as an AC20 at a longer range so they're far from useless even before their recent heat buff.