Is Fear of the Darkness really that bad? its only got a 12" range after all [taking tigerious though 24"=harsh]. The armies it really punishes are those that take static lists which bunch up and sit there near the back of there deployment, taking very little tactics to use. Tau can take etherals, but very few ever do, whilst IG have some of the best ld outside fearless in the game. You can make all you squads within the leadership bubble LD10 with a re-roll so against the darkness its still above average.
I do think its a powerful power but not quite on par imo as siren and similar