Hetzer is really a meme unit. The doctrine would need changes and the Hetzer would need buffs along with a price increase to become viable. KV-8 does everything Hetzer does, just way better and also has considerably better support units around it, and not even KV-8 is seen that often.
Comparing Hetzer to KV-8 and saying its bad because KV-8 does X is same as comparing WASP to Hetzer and saying WASP is bad, because it can't even survive 2 ATG shots and is penned by infantry while dealing low damage.
These units do NOT arrive at the same time and these units do NOT have the same cost.
Comparing them is pointless.