I have no idea where submitting comments on game balance would go, but the Forbidden Spirit power seems wildly out of line with every other combat ability. The five other powers which you might use to attack a Sin directly - Severance, Fury, Sabre, Fling and Bullet - all cost essentially 1 psyche burst in exchange for 1 attack done at CAT scale that can get on average 0-2 extra dice.
These act as upgrades over the Blast power does an attack at CAT scale, but has a chance to fail and lacks range or dice boosts. Fair enough.
Meanwhile Forbidden Spirit, in exchange for 1 psyche burst, will give you that much - a CAT scale attack with +1D - but will then keep attacking, for as long as the exorcist is willing to take whatever stress it's taking. It also gets one free chance to ignore stress.
A CAT 5 Exorcist with Fling can toss around 8 eighteen-wheelers but then have a SIN overflow, while a CAT 5 Binder can tell their pokemon to toss 8 eighteen-wheelers and unless someone shoots it with an anti-tank missile it only costs one psyche burst.