Seems like you need to train yourself against the computer AI with the IS2 first because the IS2 can certainly hit quite hard against inf like a pershing. It's certainly less reliable than a pershing as I'd say every 5th shot is a complete miss against inf even when stationary. And around every 6 shots is a squad wipe. It certainly hit inf more reliably than a panther. The persh gets a squad wipe every 4 shots on average. IS2 owns persh on survivability and they have similar RoF and penetration against armor. In summary, this is a L2P issue.
Yeah, he's good. Therefore, no one uses it.