Kv8 performs OK against team weapons thats it.
It is very bad against blobs or sole squads, becausae it targets single models instead of the whole squad. The area damge is too small, so it takes a very long time till several models die, and that is especially when the squad is moving. 1 panzerschreck can almost kill a kv8 if it keeps moving/dodging.
You cannot have all mighty tanks, that counter all infantry and game will happen only tanks vs tanks battles.
If you combined KV8 with AT infantry, result is adequate.