Its actually a good card. If an Xyz deck suddenly becomes meta some deck that can make rank 8 (cough BE) can easily put this to banish Xyz spam as long as they can be targeted. And dont start me with but it looses to a single Karma cut.
It's not the best rank 8, but Giant Grinder is certainly no slouch. The card's a lot like the imprisoning mirrors, as their usefulness varies based on the meta. One of Grinder's best selling points is that it can destroy any special summoned monster, so it's not as terrible as, for instance, the Meklord cards were during the synchro era.