Blockchain would be WORSE because you have much less of a shot at reversing and recovering the fraudulent transactions.
True, but can't you still trace the transactions as they are processed or converted into real cash?
Bitcoin tumblers obfuscate the trail
Tumbling $100 million seems slightly painful.
Blockchain doesn't seem like the most appropriate solution here because what you really care about is basically document signing. The ledger can be maintained by a central authority (accounts payable).
If a vendor sent their bank details via a signed message in the block chain then a change of bank details could be arranged by sending a new signed message from the same address with the new details. Obviously it would need to be agreed in advance that this is the method of changing payment details, then the buyer can absolve responsibility to the vendor as it will require the vendor to maintain security of their private key.
A blockchain wouldn't improve the security of sending a signed message at all it just provides a shared storage of the message.