I got it.Without it i would be screwed because now Griffith is besieging my castle with 3076 soldiers.Jay.And I have about 250 soldiers.Seems hopeless but the berserker armor is AWESOME.
I too have that Farnese quest bug.
EDIT:I killed pretty much on my own about 900 soldiers.But there are still about 2000 and next time I can`t go berserk

.So I will have to abandon that castle