Hybrid specs typically aren't very useful for leveling. You miss out on the powerful talents at the top of the tree, like Combat Potency, Mutilate, Find Weakness, Cold Blood, Deadliness, etc. Hemo is a pretty bad leveling spec anyway, its damage output is much lower than Sinister Strike, especially when you're leveling as you'll have about 1/3 the attack power required to make it equal to SS energy efficiency.