Folks,
It seems that we are overly complicating the issue - big time!
Aetius is not being asked to do an initial aircraft evaluation - that has already been done and the type selected. He is being asked to do post-production acceptance flying which, if I may be pedantic, is not test flying but rather a form of check flight that involves very little more than normal operations.
The client airline needs to satisfy itself that the manufacturer has an appropriate quality control mechanism that adequately addresses all of the test flight issues - aerodynamics, systems, propulsion, performance and build standard. If the client's acceptance pilot wishes to observe that test flight, then so be it.
However, the client airline's pilot representative is assessing suitability of a particular aeroplane for line service after having been satisfied that the manufacturer's test pilot has confirmed that that wings are of the right shape and bolted on the right way, etc. The real skill required is not the perfect rudder doublet but rather superior knowledge of the contracted standard of finish, systems functionality and operation in abnormal situations and, most importantly, a very good knowledge of the documentation to be provided with each aircraft for both flight operations and continuing airworthiness.
Everyone has a place in the sequence - let us not confuse who does what to whom!!
Stay Alive