It is a powerful spell but lacks versatility. More often than not, early in a campaign a S8 hit will have an identical effect to a S5 hit, which sounds significantly less impressive. Sure, the spell does excel in picking off henchmen (especially stuff like ogres) and even recently promoted heroes, but later in a campaign when a single hero can take on waves of henchmen, your "ridiculous" spell is just that: ridiculously useless against the enemy's only real threat. When you're facing a rampaging vampire, you'll find bringing along a bow will help you more than that eagle's wrath.
The majority of the time I'd rather have a spell like warpfire (or even summon squirrels). Much easier to cast, and I frequently get multiple injury rolls with each, something "Wrath" will never produce.