Who is who?
DFC, I understand your argument but is it all that simple.
As said the pilot is not required specifically to undertake training on a new type (differences training aside) however the PIC is required to satisfy himself that he is fit to undertake the flight. Flying a type outside of his experience without satisfying himself that he is fit could put him on the wrong side of the line.
If the non-instructor but experienced person on type is acting as 'safety pilot' and is there to only share knowlege or take command if required that will satisfy the requirement in my view. I'm not convinced that the safety pilot can act as crew and log anything. If I'm right then the pilot new to type logs PIC. The safety pilot will only log PIC only if they are required to take over.