No unit should be selfsufficient. Now if you didn't build and vetted an army to support your KT, I don't know what you are expecting from it.
Most of the Allied AT units that count vs the KT are pure AT, which means your infantry and Raketen and more than capable to hurt them and force them off. And if you face a pak of medium tank that are going to circle and kill your KT the answer is simple, KT wasn't the solution to your problems.
KT armor Works well if you keep it facing your enemy.
noone expected that the KT kill the enemy alone. NOONE. But as player u expect that the KT isnt a trash tank which is so slow that it cant reach the enemy front untill it exploded.
often u drive..shot one time and get 3-5 penetratet shot into your KT. or a sprint con dmg your engine and now you can drive with 1km/h into your base.
armor was nerfed, dmg was nerfed, AT guns and TD gets stonger since last patches...so..yes...it isnt worth the cost anymore. you will be better with panther + p4 / jp4
because now u get the range to shot back to the enemy tds