The math on the base items (no mods enhancements or armorings) is this:
Dark ward: increases shield chance by 15% until the timer or charges expire
WH Shield offhand with no mods: 5% shield chance, 20% absorb, 449 force power
WH Generator offhand with no mods: 649 force power
Tank gear with shield and dark ward (assuming the gear gives you 30% shield and 50% absorb):
45% shield chance x 50% absorb = 22.5% mitigation on average from white damage attacks
DPS gear with shield and dark ward:
20%shield chance x 20% absorb = 4% mitigation on average from white damage attacks
DPS gear with shield and no dark ward:
5% shield chance x 20% absorb = 1% mitigation on average from white damage attacks
I'm inclined to think that with DPS gear, 200 extra force power will increase your force damage way more than the 4% mitigation will reduce white damage, and that you'll also be using force abilities way more than you'll be taking white damage hits (meaning generator would be infinitely better) but it's just a guess.
In tank gear you almost obviously want the shield.
I know that we have had our differences in the past, but you're spot on with this. The problem with shield gens in PvP comes with the ineptitude of tank design in PvP in SWTOR. There is rarely ever a situation in PvP where wearing a shield is beneficial. Even in a full tank spec, while wearing full tank gear. I really wish that BW would adopt the PvP tank design that they used in WAR. That being incredible mitigation, mediocre damage, emphasis on taunts, protecting healers, and control through knockbacks and CC. As of right now, it almost seems like the dev team is at a loss as to how a tank should function in PvP. Tanks do have some of the capabilities that I described, but without the added survivability. In all honesty, I hardly see any defensive increase from running a full tank spec over, say, a 0/27/14 spec. That, IMO, is a problem.