Jagdtiger is the go- to solution. Fight fire with better fire.
However, frequently using smoke to deny LOS to the ISU is also a decent(and nondoctrinal) solution, forcing the ISU to either cease firing for a while or move out of the smoke, closer to your AT weapons.
Except that the ISU offers far greater utility than both the Elefant and JT. Further the Elefant and JT are even weaker now than they used to be.
The ISU can just switch over to fight infantry and tanks quite reliably. While with the Elefant and JT you are stuck to fight off tanks. And even that doesn't work good any more since mediums can swarm you easily, even with support.
Any competent player will just switch to infantry and/or safe for a medium tank horde and the German super heavies are useless. Thus you are stuck with a quarter of your pop being useless. Meanwhile the ISU can switch over to bombard infanty.
This leaves you with the Panther and JP IV as OKW which in my opinion have also been a bit overnerfed. Ostheer at least has the StuG remaining.