Agreed, your spec isn't going to matter too much with three locks. You'll most likely just end up ripping through things with triple shadowbolts, which will do the job in one or two casts even if you're not specced for them. My 5-man team includes 3 locks, whom I leveled as Affliction ... but when I wasn't AOEing, I was shadowbolt nuking without a single point in Destruction.