Figured some smartass would point this out. I wasnt comparing the pens of both tanks, only the health.
Penetration decreases with range. Especially for low-velocity guns like the ISU 152 has. The ISU-152 will still not be a long-range anti tank gun like the elephant, but now it won't be so easily killed from up close. It might now be actually something worth getting in a 1v1, rather than a free vet bonus for panthers or tigers.