Honestly, I don't see a reason to.
Monks may be worth a spot on one or maybe two encounters due to their higher dps. I wouldn't bring a Dragoon over a Warrior ever. In the grand scheme, Warriors are simply much better all around than either of the other two melee jobs. Most of the setups in my LS and outside are either range stacked or Warrior stacked. The best tank job is also the best all-around melee job. Their damage, their AoE damage, and their survivability in combination makes Warriors the best choice in most cases. I understand they are making some changes for Paladins, but how about for Dragoons and Monks?
I don't want to talk about range v. melee, just simply melee v. melee in this thread.