Indeed. He starts by saying "If an attacker succeeds to put himself between a merchant and the RaiBlocks network he can ... ".
Well, I say : Hold your horses cow-boy, if you successfully performed a Mitm attack, then you have already won, no matter the crypto currency or bank. For example, you can just replace all bitcoin, xrb, eth, ... addresses where your victim wants to send funds by yours.
That's not true of contemporary cryptocurrencies like BTC and ETH. A man in the middle does nothing to break the security as the signatures for a tx cannot be forged. XRB has a weakness for MITM attacks that other cryptocurrencies do not.