Certainly I have done many a manual loadsheet in my time and it was usually either necessary or that a computer-generated version was going to result in a very long delay.
I could usually put a manual loadsheet together in something less than 10 minutes. The easiest version that I ever got involved in was the Laker DC-10 loadsheet. We had a plastic whizwheel provided that did the job very quickly.
It was my experience that the modern button-pushing F/Os had no idea of where to start and might just as easily have been asked to prepare and interpret Gordon Brown's version of world economics as presented to the World Bank.
I suppose it depends on which organisation one works for but preparing a manual loadsheet is not exactly rocket science.