42-004 says that the plug can't be less than the "conductors required". That's different than the ampacity of the conductors because you can always oversize the conductors without changing plugs. If you couldn't, engineers wouldn't be able to inflate the cost of the job by going "above code".
If the size of the cord end bothers you that much, change it. Why would you run #6 wires to a load that needs a maximum 24 amp circuit ampacity?
