what is difficult in balancing the isu152 is because ther is no other vehicle quite like it, closest id say is elephant because of the cost, timing, hp/armour etc.
elefant - excels in AT but no ai
isu152 - Decent AT but excels in AI
if isu152 maintains strong AI, then nerf its AT or remove AT shell and make it reliant entirely on AT support, similar to how ele relies on entirely on AI support
Actually, closest to ISU is KV-2, both are breakthrough, primarily AI defense line wreckers with average AT and very low RoF(KV-2 has low rof in tank mode).
ISU can bounce off OKW P4 and that's a medium tank.
Meanwhile there is no allied vehicle in game that Ele can bounce.
AT performance is quite significant here.
We could go KV-2 route with just 1 round, low pen and high deflection damage, but then again, why would you go ISU over cheaper and more reliable KV-2 that can do the same things ISU can, but fires almost twice as fast and more accurately in arty mode?