Is your argument that Bangladesh would have been safe if they were using a blockchain? Given their revealed security practices, I'd be surprised if they had the ability to secure any private keys from being revealed - and they would have had even less recourse with a blockchain based system (though admittedly, their recourse is limited even now).

I don't think so. They would have lost ALL if the private key would have been compromised. In this case they even managed to block some transactions and recover quite a big chunk of money.