You can beat PD. Here is demonstration how;
Your top priority is to stop PD player from expanding too much,avoiding this step will lead to defeat. In 1 turn if you are close to each other,stop his expansion like Ukraine vs Germany,attack Austria,Sweden,etc. 2. Take countries as much as you can.More countries more money and units,attack him at low defense city's,break walls so that he can't defend every city,take important city's from him,of course they will be good protected but then attack with more units.I have beaten many PD players with GW,Blitzkrieg,SM,PD vs PD, you can also try Ukraine imperialist,so good really,you can buy tons of tanks,attack with lot of units,and always have money.