In all the years I got hauled up and down our masts, I never thought the halyard would actually fail, more likely the attachment point of the pulley. All our halyards were external, 1/2" double braid dacron, we replaced them maybe once every 5-8 years...and that included many, many miles of ocean sailing, with many more pounds of pressure on them than I could ever exert being pulled up! Our halyards were constantly exposed to the elements for years on end. That's where I learned to do the 'pick test', pick the strands with your fingernail and if some fibres break, time to take action!
Of all the things that ever broke...main headstay, fore staysail and jib pulley, it was always hardware, usually a fatigue issue after a few thousand miles.
Kind of like tree climbing, I would say its very, very rare for a rope to break, more likely to be the tie in point.