As is well established, spell pen wasn’t useful in classic PVE except for a couple of bosses — but that’s not the case for SoD.
So, aside from warlocks who get a class trinket, our caster trinket options are:
• Miniaturized Combustion Chamber
Now, considering this…
Gnomeregan Boss Armor and Resistances
Doesn’t this mean the WSG trinket is BiS on the last 4 fights in Gnomer? In classic, if a boss had resistances, 1 spell pen was equivalent to 4 spell power, until the boss’ resistances were negated to 0, at which point spell pen became useless.
If the same formula applies in SoD, that means the WSG trinket provides +80 spell power equivalent, as the last 4 bosses get reduced from 20 to 0 resistance.
All that said, if anyone in your raid has resistance reducing talents, or Mekkatorque’s Arcano-Shredder, the WSG trinket becomes useless.
Also note: Curse of Elements only applies to fire and frost spell schools. This is irrelevant to shadow priests, for example.
This is all thinking out loud. I can’t confirm anything here. Any input or discussion is welcome!