This is soooo true... My fire/fire blaster hit 39 and started trying to hunt in PI in a duo with an emp. defender. All I can say is "dicey".
Where my alpha-strike used to decimate groups completely, now it takes out minions and leaves 4+ Lt's and the Boss standing there really ticked off. Even running +2 mobs I'd say my death rate against the Nemesis in PI is 20%. Way, way too high for me so I've stayed in the sewers as much as possible.
At 39 my AOE is certainly not what it used to be...