Thing is, the KV-1 is meant as a breakthrough tank for infantry support. Much like Tiger said - useful for pushing through defenses (with heavy crush) and to support infantry advances (also the reason why the KV 1 call in is on the same tree as "Inspiring Speech", which acts as a support ability for infantry units).
For a 4cp unit, the KV 1 performs pretty well overall.
The reasons why there is no KV 85 upgrade are pretty simple:
- the KV 85 doubles in its role with the IS 2 too much. Both are meant as heavy breakthrough tanks for lategame situations to stand up to enemy elite infantry and tanks.
- to fit into the soviet upgrade scheme you'd need to be able to upgrade KV 1 tanks to KV 85s. And this makes no sense, as KV 85s were highly modified from the original KV 1 tanks
- Breakthrough already offers a lot of utility to soviets and helps out with various types of strategies, and getting the KV 1 and KV 85 would make it even stronger
- The Soviet upgrade system for heavy tanks will be reworked in the next release, so the KV 85 will fit even less compared to the current release version
The KV 85 is likely to be featured in a reward doctrine for Soveits in the future.