I bet the shock current through the nerves touching the metal causes more pain/sensation at that location, but that the current is flowing through your entire body is the actual hazard.
I've said this before: 'working hot' is a design failure. Think about it, in a very generic sense _everyone_ works 'hot' all the time. I don't shut off the breaker to plug my toaster in; and shutting off the breaker is itself an operation on a live electrical system.
In some cases simply throwing a switch is considered 'working hot' and requires PPE or using some sort of remote operation tool.
So what is the difference between throwing a light switch and 'working hot'? IMHO is the the risk of coming in contact with live conductors or causing a non-contained arc flash, or some other reasonably expected risk that would be eliminated by shutting off the power.
Well if (for whatever reason) a facility cannot tolerate shutting off the power, then the system should be designed to be worked upon with no more risk than flipping a light switch or plugging in a toaster. Such a system would of course be more expensive to build in the first place, but then you could leave the power on while the electrician could work safely. If it is so desperate that lights must be left on, then you should have 2 lighting circuits supplying every area so that you can shut one down and still have light. If there were demand, then breaker panels could be designed to have finger safe buss stabs and breakers. etc. IMHO systems should be designed so that there is no need to 'work hot'
-Jon