That is really weird OP. I have both PS2 and PSS on different sets of rims and in the same sizes (OEM). My PSS have more grip under all conditions (especially wet/cold)... so much so that I use PS2's when I want to drive the car with less grip.
Check your tire pressure. If they are not hugely overinflated, then you probably have a defective set.
Conti DWS are good tires, but they do not have the grip level of Conti DW's or other max. performance summer tires.