Melee (and I'd say tanks as well) are almost completely useless in Slaughter mode. You have two options:
-Sit with your team and pray that another dps overextends into your territory so that you can try and get a kill, all the while SMNs, BLMs, and BRDs pummel you from their side of mid (also have to pray that your healer(s) can heal you and aren't busy with other people)
-Try to attack towards the enemy team and be instantly destroyed by the 24 enemy players.

Melee had a place in Secure, really isn't much point in bringing one in Slaughter.