I'd wager that's why they nerfed it. Sac and Supremacy were near identical in terms of single target dps, sac was taken only for cleaving with Havoc. Which is arguably too strong when used properly...two 500k chaos bolts?. I don't mind this nerf too much, but I was hoping for a slight single target boost.
Edit: All this really does is make the talent more of a choice again. Single target? Take Supremacy. Cleave? Take Sac.