You should test Foe again I think, I tested it recently and Foe brings 6%-7% magic damage, and 13%-14% with BV.
Entire 10 minute fight??? Foe drains mana...
If You spend ALL your mana using Foe, You are gonna be able to keep it 31% of time up...If You have to bring Mana or TP regen that 31% is reduced easily to 15%...
10 minutes fight, Foe 31% time up, 3 minutes and 6 seconds bringing +6-7 % magic damage is NOT massive...
Foe is pretty good since DPS checks can be aborded with Foe and BV, but It's situational, not massive...
