I think it comes down to how things are packaged:
The OEUs find out how things work.
The T&E sqns, with the support of a phenomenal amount of scientific experience, find out how things fail.
As long as everything fails 'safe', which package, do you think, gets accepted most readily.
As I like to tell the people I work with (and for): It's not the job of Flight Test to break the aircraft, it's our job to point out where the aircraft is broken