Panther is supposed to counter all medium tanks and can be spammed.
It supposed to counter tanks and that includes IS-2.
It's also way cheaper than IS-2 and does not require CP.
It more expensive than FF/M-36/SU-85 that also do not require CP
IS-2 is supposed to be countered by Elefant, Jagdtiger, Konigstiger, Jp4s, Stugs, Pak 40s, Pak 43s and finally Schrecks. IS-2 should indeed counter panther, germans have a lot more options to deal with heavy tanks AND THOSE OPTIONS SHOULD BE UTILIZED, not abandonded. You just want to spam one unit to kill everything, and that's not how the game works
Panther is not main battle tank. Its role is to counter heavy armored vehicles.