ARC/BRD can use PIE to strengthen both their debuffs as well as their damage, so it's fine to make it reliant on PIE because you are going to want your debuffs being consistent. The only other class that can make as much use of PIE is LNC/DRG, GLA, MRD and PGL need to decide whether they want better and more consistent debuffs or more damage, whereas ARC and LNC can have both.