Mostly Bull sh it
Properly setup the flight differences range from totally undetectable to a little bit
The real problem is that the rest of the airplane is also . usually different
This makes for instant "expert" appraisals which are meaningless.
The setup for a good foamie that is just hovered and hovered till the batts play out - is all on line - or close to it - it is an easy setup to do
but if you want to prove the answer-- build some foamies and just move the wing -up down -changing nothing else.