Not watched the game but I discovered when getting bulletins with my friends in custom games that ISU loses in a frontal engagement to the Tiger every time. 2 Su85s are much better.
Take an IS2. Remove turret, remove ability to fire on the move, increase inaccuracy, slow down reload, reduce penetration, remove the armor and replace it with su85 armor values, increase range to 100. Voilah, you have an ISU152.
Ie. Yes it's absolutely guaranteed to lose to a Tiger from the front even if the Tiger just drives to it from 100 range. A single SU85 is more of a danger to any german vehicle than this thing. Didn't watch the game but if you expected an ISU152 to do anything against a tank, that was already you screwing up.