Nicely Put, NS. To introduce another angle, surely it has more to do with the physiological capability of individual pilots? Outside of aviation, it is recognised that a certain percentage of employees have health problems from working different types of shift patterns. Equally, some employees recognise that the shift pattern they are on is not good for them, however they continue on to their detriment for either financial or personal reasons. None of these guys suffer from the complementary debilitating effects of jet lag on top of the shift patterns, which must be an extra physiological stress - for some.
Some will not be able to handle the stresses of short haul loco flying in the medium to longer term - equally, long haul is very destructive physically and mentally for some people. Plus ca change.