Bringing human error into the circumstances opens a whole new arena. No piece of equipment is idiot-proof as no matter what piece of kit is on the end of the winch cable, it will only ever be as good as the person working it.
Any means of attaching a person to a cable and winching them to an aircraft is hazardous. Granted, different methods have different advantages and disadvantages, but no matter how well you design something, someone somewhere will get it wrong. That does not always mean the equipment is the link in the chain that was at fault.
IMHO the more complicated you make things, the greater the likelyhood something will ruin the day. The biggest single advantage of the Nato Strop is its simplicity of use.
Obs cop