Ye sure open world you can exploit some situations, even with a buddy. Im not worried personally for locks, I will lvl up as a duo with my bro.
Its for the health of the game , plus for locks. Sure you can pick another spec in pvp. But it can feel bad when it feels mandatory to be sl sl because its the superior pvp spec.
As for the pet aggro part, you have demonic brand so , its less of an issue I figure.