Personally, I think the IS2 is crippled by being originally designed in COH as an analogue to the Tiger 1, when historically it was closer to the Tiger 2 in terms of armor protection and firepower. If I could redesign the unit from the ground up, I would make it a heavily armored, slow RoF vehicle with the same main gun damage stats as the KT (Slower reload obviously.) To compensate for slow RoF, it should instead have faster movement speed than the KT, and maybe a wider AoE on each shell so it damages infantry in a wider radius (but doesn't kill anymore than the KT does.)
It would obviously have to be priced around as much as a KT with these changes though.
I get why people are advocating for a change like that, but gameplay-wise I'd argue this isn't a very good solution. If you want a hard-hitting, heavily-armored, 240 DMG vehicle with slow reload to compensate you already have the KV-2, which fills this niche quite nicely. Turning the IS-2, or better the 122mm main gun into a KV-2 clone would rather remove some of its uniqueness IMHO, not add more to it.
At the moment, the IS-2 is pretty much a Tiger I analogue in terms of performance - a bit worse at AT duties (taking both survivability and damage output into account) and a tiny bit better AI-wise. It also already has a much larger AoE compared to the Tiger I, which sources most of its AI DPS from the fast reload speed in exchange for hitting less models at once.
So in terms of "flavor" the differences you propose are already there, and although scaling the IS-2 to be more of a Tiger II equivalent is certainly possible, I don't think this would change anything with respect to how viable it is in teamgames. The same counters that make it a sub-par choice in larger game modes (at least according to those who play these modes) would still hard-counter it in almost the same way.
Overall, I'd say the IS-2 is fine the way it is, even though it might not be a 100% accurate representation of the real-world namesake. The only thing I'd change is maybe to make the vet-1 skillshot a bit less telegraphed and awkward to use. This alone could give it a huge boost and also make the 122mm cannon live up to its name - at least vs infantry.