If a miner gets hacked, then their blocks will go to the attacker, or they won't be mining. Blocks will be mined more slowly and transactions may take longer for the same number of confirmations until the miner comes back. If a bank gets hacked, people steal money enormous amounts of money by directly changing their ledgers. I don't see this as some sort of a loss for cryptocurrencies.

I'm not sure what you mean by turnover although you might want to learn more about bitcoin before you rail so hard against it.