Not only that, they nerfed Orb damage in 1.10. In 1.09, you still needed a pretty good aim to kill with orb. It's the same with fireball, just requires more finesse.

As Kuja said in some thread a month or two ago, 1.10 is requiring more skill to PvP in due to the fact most of the 'cheese' skills have been nerfed (WW, Orb, Hydra, Piercing Guided).

If you think about it, Fireball would be easier to hit with in some respects... I mean:

a. It's Faster (Movement-wise)
b. It has no 'cool-down' time.
c. It's range goes beyond the screen.

If you got Hydra to help herd them, you can lay down a pattern to catch them, or the Hydras may even stun them, making for a simple kill. I fail to see how Orb is still a superior spell.