The reason you cant I think is because the server is not fully 1.9 yet, so until at actually does fully update to 1.9 (Which I hope it doesn't due to the trash hitting cooldown thing) then you wont be able to have things in your left hand and pvp with the cooldown and stuff. Basically features in 1.9 that would affect other peoples gameplay in 1.8 like duel wielding and the cooldown wont work yet due to it not being fully in 1.9, I think lol.