Wire transfers are also hard to reverse, but banks have security ceremonies around them to prevent misuse, and good luck to you if you want to pay a $20MM ransom with an international wire transfer. Even if you were able to find a banker who wouldn't call the FBI on you, the recipients of the transfer are exposing themselves to significant risk of capture by interacting with their local banking system and by providing you with the details of their account.
Cash being convenient for small transactions and difficult to use for large ones is a deliberate feature. The point is to strike a balance between usability and vulnerability to misuse. E.g., you have to declare when you're moving more than $10K across an international border, and it's actually hard to smuggle that much cash due to the weight and bulk. Gold is also heavy and bulky, which is an important security feature of Fort Knox (even if you break in, how are you going to abscond with tons of gold bars?).
It's hard to move cash, but it was harder to move gold ergo we should stop using cash because it's easy for criminals to move and use gold instead. That's the line of reasoning at play here that is espoused by this argument.