I agree with that statement. When I first started I was all about power, power, and more power. Boy did Cressy screw me over!I think one of the reasons many teams are easily stallable is that people have taken "DP is very offensive based" too far, by assuming they can simply win by brute force and nothing else.
MixApe has helped me a lot. Also Choice Specs Gengar seems to help out, as I KO many weakened Cressys with a Choice Spec-ed max Special Attack Shadow Ball.
EDIT: Calcs - Max HP/Min Sp. Def Cressey
Damage: 350 - 412 HP (78.83-92.79%). HP: 444
I admit I use a Swampert lead due to it's ability to not get OHKOed by anything not related to grass. I'm not that dumb to even consider leaving it with anything that could be running HP Grass. Hence why I have two decent counters to help Swampert: My Tangela provides a defensive wall while taking out other Swamperts, Hippowdons, T-Tars, etc. I also pack HP Fire for Skarm and Levitating Brozongs. Togekiss is my special sponge and just murders some people (I think I went on a 3 KO streak with Togekiss running Air Slash/T-Wave/Body Slam/Wish).