Barbarian magic suppression skills...

Well, darkness is still somewhat exotic for the Elves. And besides, you forget that there can be other races on the map besides the Elves;)

Of course! Otherwise, where would the Elves get Berserk, Subjugation, etc. (perhaps from a city of dragons, for example), but still (I repeat) not choosing Darkness against the Orcs is unwise! And for the Orcs not to counter Darkness is suicide;)