Or it could be because the skill is underwhelming AF and we would like it to be less so. It has nothing to do with playing WHM to its full potential but rather that the skill is just a big let down, especially when compared to skills we've gotten earlier. Assize is 2 confessions worth of Heals+Damage+MP return, Thin air gives free spells for 12 seconds, Tetra is a free burst heal, Asylum is a fairly potent AoE regen and are all arguably better than PI.
PI requires at least 1 AoE heal to go off and heal people for it to even be active and then you have 10 seconds to make use of it or else you lose it. In a Dungeon setting, this is unlikely to happen since most damage is directed at the tank and the few times anyone else does gets hit, a single AoE heal will either be enough that PI is just overheal or in the case of medica 2, would just cause it to waste the regen effect. In raids, the heal is so underwhelming, that unless it crits at 3 stacks, I've often found myself still needing an additional AoE to fully top people off after it's use.
Defend it all you want but please, don't insult people because you feel it's fine.