Preprogrammed route theory is a red-herring, since the alleged route flown by the airplane makes no sense. It is a zig zag.
Could an unqualified person (i.e. non pilot) looking at the HSI and heading towards a waypoint have done that?
Get real - today even 8 y.o.s run flight sims on their tablets. Doesn't take a rocket scientist to work out that if you select a value in the HDG window on the MCP - that is the direction the plane is going to fly. But to know that the wp you see on the HSI is in fact a virtual point somewhere over the ocean - that is a different story.
Mid air collision = fuel patch on ocean.
Pilots become incapacitated. Plane make erratic climb/descent.
Someone attempts to take over controls (ala Helios) - pax, cc, maybe someone who is going for a ppl/cpl? Doesn't know how to operate radio (hence garbled RC). Doesn't understand nav displays (hence goes from wp to wp, hoping it is an airport).
Collision explains why local authorities reluctant to share primary radar data.
FFS, a patch of jetfuel on the ocean at LKP, you can't just dismiss that.