I'm not fussed about who it is that sets the standards, as long as there is some standard set.
We wouldn't let people go solo in IMC without some training and an approved syllabus or demonstration of ability, why do we let those who flight test do it without some indication know what they're doing?
Not everyone has to go to a TPS and my good friend Nick is proof positive of that (in fact, if all pilots were like Nick, we'd be out of business in flight test training), but you do need to know something - the question is 'what do you need to know to be safe and long-lifed test pilot / flight test engineer???
And how do you demonstrate it?