Stamina.

For my 3rd character I wanted a scroll runner/utility build. I use it to stay outta trouble when leading groups in Cyrodiil, as it's my only bow toon of my 5. Bolt escape and pew pew lets me concentrate on situational awareness.

That being said, before 1.6 this character was absurd. Post-2.0 it's actually amazing at killing DKs in melee (dual wield, with access to a huge variety of endgame sets for situationally specific theorycrafting). But nothing else. And now that speed buffs don't stack she's only 30% or so faster than every other toon.

Imagine a sorc without reliable self-shielding (I use Spiked Bone Shield, but it lasts 6 seconds and relies on stamina, and when people synergize it the self-effect particles disappear, so I don't know when it drops). Spell resistance is poor.