The PDP-70, as we should know, is available to two mercs - Vasilli and Redeye.
When people play Vasilli, they almost never choose the PDP-70 over the MOA or even the FEL-IX. I actually have the best PDP loadout for Vasilli in Cobalt and I always pick the bolt actions over it anyway. So in comparison to the MOA and FEL-IX alternatives, the PDP-70 looks like it needs a buff.
And when people play Redeye they... Wait, who am I kidding? No one plays Redeye! Partly because he is so bad in combat since his weapons of choice are really not very viable. His abilities (smoke grenades and IR goggles) vastly outmatch Vasilli's motion sensors, so it's pretty clear that the reason he isn't used is because of his poor combat abilities. In that sense, it seems logical to buff his weapons, including the PDP-70.
So between both mercs who are able to take the PDP-70, it seems that the PDP is far from competitive in its ability, let alone overpowered. So why is the PDP-70 receiving nerfs every single time a weapon balance patch comes out? First we had the removal of its insta-gib, then a drop in its firerate, and now a drop in its magazine size.
So to conclude this post, I really don't understand why the PDP-70 is getting constantly nerfed, despite its clear inability to provide effective combat abilities to either of the mercs who can access it. If anything, it needs a buff.