The curse SLA in DA tree is not very good it has twice the CD of it's spell counterpart. All the SLAs in the tree scale poorly because they don't utilize empower, maximize or intensify. Bane and prayer have short CDs and low mana cost, they could be useful when receiving the damage buff from curse. Curse however only applies to one target at a time while bane and prayer are AOEs. I think it would be a reasonable change and considerably better gameplay to allow the curse SLA to apply in an AOE.