If Dim Shield is OP then PC is not related to the answer.
Is it?
Assume quanta is colorless.
Dimshield will only be nerfed by the inclusion of PC if the inclusion of PC makes PC usage more widespread.
However, including PC that is as "balanced" as current PC will not make PC usage more widespread, because the additional PC will only become substitutes for current PC.
Only including PC that is overpowered (SoFo) will increase PC usage because the overpowered PC (SoFo) will substitute currently "more powerful" alternatives to PC (survival and win-conditions).
Adding PC if PC did not exist would nerf Permanents.
Adding balanced PC to a game that already has PC would not nerf Permanents.
However, quanta is not colorless. We have 12 elements, only few of which have PC.
Because of this, certain decks (mono-this and mono-that) cannot include PC without revamping the quanta base. For these decks, PC might as well not exist.
Thus, the inclusion of PC in non-PC elements will, scaling to the amount of permanent usage, increase the usage of PC and thus nerf all targetable permanents.
Let's just stick more PC into the game.
Because cards like Gravity Shield, Empathic Bond, and Nightfall are just sooo OP, right?
Let's assume all creatures are Graviton Mercenaries.
Graviton Mercenaries are currently more resilient against creature removal e.g. Shockwave, Rain of Fire, etc. than things like a Crimson Dragon. Let's say an extremely powerful creature with stats 50|50 comes out. To counterbalance this, we create a zero-cost card "Bomb" that wipes out all the creatures on the opponent's side of the field. If everyone who currently uses Shockwave, Rain of Fire, etc. replaces those copies with copies of "Bomb", then yes the resilience of Graviton Mercenaries will fall.