Simulationcraft for Sage/Sorcerer

[NegativeChirality]

So I was curious enough to do some expertise scaling "by hand" for full Champion and full Centurion gear (with completely default mods / enhancements / etc), for a Hybrid spec (though I only have like half the datacrons and didn't put in the relics correctly, so YMMV for your own character).

In full Centurion Gear, scale factors For DPS are
Will: 0.27
Crit: 0.17
Alacrity: 0.07
Power: 0.24
Surge: 0.33 (note that Centurion gear has zero surge on it by default)
Expertise: 0.11

In full Champion Gear, scale factors for DPS are
Will: 0.29
Crit: 0.17
Alacrity: 0.07
Power: 0.26
Surge: 0.22
Expertise: 0.10

So in terms of DPS, at least for mid-level PvP'ers, Expertise is only better than Alacrity, in terms of DPS.

For example, I have Centurion Wrist and Waist. Switching to Columi Wrist and Waist increased by DPS by ~4% but increased damage taken by 1%. Upgrading to Champion Wrist and Waist increased DPS by ~1%, but decreased damage taken by ~0.3%.

Conclusion: expertise, at least for someone around 600 expertise, is a shockingly mediocre offensive stat. And a shockingly mediocre defensive stat, too.