Just as valid a statement as "Most airplane accidents happen while taking off or landing". It is a valid statement, but doesn't really tell the complete truth. As far as this thread is concerned, all CSIT (controlled sailing into terrain) incidents should be ignored. Any non-trivial contact between boat and ground is going to be an accident regardless of the boat or crew types.
So if we take out land as an accident factor in comparing bluewater with non-bluewater what remains? I would put Captain, Crew, Weather, Equipment, and Navigation at the top of my list and look for differentiators in those categories.
I would say You 'hit' off target.
The reson for the 'accidents' are mainly caused by handling/captain/crew errors and not related to if the boat was a 'Blue water' boat or 'Coastal' sailing boat.
As to follow Your logic of safety - sailing versus flying: Flying is by far the safest as no one have ever been left 'up there' -they all come down! However quite some sailors have been lost 'out there'.