Belial's adds and Azmodan's Hell Grasp are not that predictable if you don't have enough dps to just power through them. Show me a video of someone killing them in blues and you'll invalidate my argument completely.
I thought Hell's Grasp was random myself. Turns out the first 3 spawn on the edges. Next 4 spawn beneath you in about 5 second intervals. I used SS + Tactical Advantage to outrun the pools as they expanded. Dancing around the edges of the previous pool let one control spawn locations as the pools can't spawn on top of one another. Unfortunately, the bug that had the diameter of the pool exceeding the graphic did add at least one random element.