Actually ISU-152 were largely pushed by propaganda. To some extend as much as the Tigers. This fear from heavier german tanks had to be overcome, thus the Zveroboy was pushed. The Russians usually used 4 ISU-152s together to get a decent rate of fire out of the vehicle(s). In actual combat there are of course some situations where the did their job well, but with a rate of fire that slow, my bets go on a Panther, which could just as easily defeat the ISu, with better optics and 6x the rate of fire.
Models being constructed throughout the war doesn´t necessarily mean tehy are superior. For example the Panzer IV while being almost outdated was in production til the end of the war, for the sake of having a tank in numbers.
It more depended on who shot who first. The ISU-152 was very powerful, and was usually used in prepared ambush positions which means it usually got off a shot before the enemy could find its positions.
A panther could have a rate of fire of 30 rounds a minute, but that wont protect it from being hit by an ISU-152. It would be an advantage however for a second panther following the first, as it would probably knock out the ISU-152