The IS-2 and KT can take hits from anything but the dedicated tank destroyers. The Churchill variants can take shots with their HP. The Tiger on the other hand - while lacking the HP pool of the Churchills - is more reliably penetrated by what I would call "middle class AT" (Easy 8, T-34/85, lend lease Shermans, Comet, M10, on shorter ranges even by the Cromwell). These vehicles all struggle with the KT and will seriously threaten a Tiger from the front. Two will easily finish it. I´m just asking for a bit more frontal armor to reduce the chance of frontal penetrations. Currently that happens quite often. 30 or so points to the frontal armor is totally adequate.
Also you still haven´t told me what the Panther is good for when StuGs totally out-dps it. Iirc the StuG reload is 4 seconds, the Panthers reload is 6.25 seconds. For a 640 HP T-34 the Stug will need 16 seconds, while the Panther will need 25 seconds. With the ready aim time and other factors this might differ but only marginally so.
The Tiger 1 should get penned frontally 10/10 times by all these "Middle class AT tanks" you listed...