I'm kind of lost here? Are you complaining that JT is not good at destroying tanks or what?
It is impossible to defeat Jagdtiger with ISU-152 in 1on1 scenario. Infantry does nothing to this tanks so its OK to neglect their influence. You need at least 2 ISU against JT and even then odds aren't 100% in your fauvor. You can even ignore AT guns to some degree as they usually don't penetrate.
This stun thing is clearly a glitch or bug of some sort.
Impossible to defeat more expensive, fully dedicated AT unit with built-in stun with a AT and AI (possibly the best AI option in game),cheaper,earlier unit on a head-on engagement? Sounds pretty reasonable, like kubels losing to M20s amirite?
The stun thing was implemented to counterbalance Jagdtiger's penetrating shot, not a bug or glitch.