An amazing level of blinkerdness being displayed by some here.
I don't think anyone is disputing that both thrust and pitch affect both speed and flight path. The question is which produces the finer control and is more appropriate. The answer to that, like so many things in aviation, is - it depends.
It depends on:
a) the characteristics of the aircraft you are flying
b) the critical task you are trying to achieve.
I'm afraid, NoodleAir, that your unswerving reliance on "Aerodynamics for Naval Aviators" as the bible for all things is somewhat misplaced. It was written in the 60's for - surprise, surprise - Naval Aviators. They were flying machines that were, by today's standards:
-Small
-Light
-Low wing loading
-possessing a "sharp" drag curve, i.e. drag increases quickly as you slow below Vmd
-often had flap blowing systems that make lift directly related to engine power setting.
-And their critical task was landing-on to a carrier; a visual approach flown at considerably closer to the stall speed than would be used for a civil aircraft.
With the exception of the last these characteristics are similar to a light propeller aircraft of today, and I would be the first to say that the best system to use in those is pitch for speed, power for flight path.
However, we are discussing modern transport jets. These are relatively:
-Large
-Heavy
-High wing loading
-with a very flat drag curve
-No direct relationship between lift and engine power/thrust setting.
-Whose critical task is a precision instrument approach to low or no visual minima.
For these 40 years of line experience from all manufacturers has shown that the best technique for line service (on approach) is pitch for flight path and thrust for speed. Which is why it is recommended in the manuals, taught at all the schools and used by the automatic systems.
Your reference to test pilots is unfortunately a red herring, because many techniques are used in test flying to enable repeatability and measurability against requirements that are different from line flying techniques. In this specific case, if you are trying to measure landing distance, speed control is more critical than the actual touchdown point which will be recorded by the cameras, so the more precise control is used.