I've been ravaged something serious by a DDOak. With Sleep Powder, it reliably gets free turns to DD, and if it gets two (which with its bulk isn't terribly difficult), it completely smashes teams not carrying Heatran. I really don't want to have to bring a Heatran on every team just to deal with it. Also, the potential for it to run EQ to handle the likes of Heatran and Cyclohm is terrifying.
The only things that can really break it offensively after a single DD are Strategem who hits for ~70% with Paleo Wave. Cyclohm can smash it if it can get in before the DD to Draco Meteor, but EQ simply demolishes Cyclohm, so..