As your party advances in level and gets stronger gear and attacks, you will begin to see the Dwearians get diminishing returns on their "Defend" ability. Until you reach that point, I have a couple of "bonus" tips:
1) Because "Defend" always goes first (and Dwearians are so slow) you can always tell if a Dwearian is going to use Defend when you see them jump to the front of the turn order. That's when you should focus on a different target or use Wait/Guard to get some HP/AP back.
2) Not all attacks can be blocked! Items like Molotovs and Unstable Batteries don't calculate a target's defenses when dealing damage, and there are even some skills that ignore defense, meaning the Dwearians can't do much to stop you!