I have finally figured this out. There are 3 types of games for tank destroyers and heavies. First there are those where you are on bottom 5. Those games absolutely suck. Can't damage anything because you don't have the firepower. Can't get hit because you die. Can't scout because you're too slow. Can't defend because the enemy can shoot you before you spot them.
Then there are those where you are on top 5. Those are usually really kool brawls. You can shoot and get shot at. Can defend snd attack. The strengths of you tanks are really strengths and the weaknesses are also weaknesses. There are tanks that can harm you and tanks that can't.
Then there are the ones where you are in the middle. Still fun but need to carefully plan every move.
It was really fun experience playing stock kv in a tier 9 match
Only way to make myself useful was to park the tank in some nice place where the rest of my team can use the wreck of my tank as a shield.