DDs have absolutely nothing going for them. Sure they can get 6/- DR if you invest 10 levels. I think they should be given some sort of bonus based on how many DD levels they have.
Give them some kind of useable that gives them this bonus. 1 turn/DDlevel
Level 1 DD +1 dmg +1 fort
Level 2 DD +1 dmg +1 fort +5 temp HP
Level 3 DD +2 dmg +1 fort +5 temp HP
Level 4 DD +2 dmg +1 universal +5 temp HP
Level 5 DD +2 dmg +1 dodge AC +1 universal +5 temp HP
Level 6 DD +2 dmg +1 dodge AC +1 universal +10 temp HP
Level 7 DD +3 dmg +1 dodge AC +2 universal +10 temp HP
Level 8 DD +3 dmg +2 dodge AC +2 universal +15 temp HP
Level 9 DD +4 dmg +2 dodge AC +2 universal +20 temp HP
Level 10 DD +5 dmg +3 dodge AC +3 universal +25 temp HP