Personally i think these pirate raids make a lot of sense and here is why:
they are being paid/supplied to fight a proxy war on behalf of the core world factions
That's what other factions/nations are for. Think Vietnam and such.
Pirates are too poorly equipped and too unreliable to be used as major military assets. Historically, they have been used to harass/attack shipping, not invade enemy strongholds. Even then it caused more problems than it solved, since the second you stopped paying them, they would turn on YOUR shipping.
There's a reason the only piracy today is in 3rd world s***holes and it takes the form of "pay me or I'll damage this expensive ship (which is by far the most valuable thing)". Have you looked at somali pirates? They come in tiny fishing boats armed with a few machinguns and a RPG or two. They prey on undefended, slow ships. They rarely take any cargo - because the parent company will pay to get the ship and it back. And because they'd have to haul it and sell it. Not an easy task. Even less so in space, where every gram counts.
Generally speaking, PIRATES DO NOT KILL OR DESTROY, they ROB. They WANT you to drop some cargo or give some $$$. If they take it all or kill everyone, why would anyone stop and surrender? Real pirates do not want a fight.