Parts is parts
I have never taken apart higher end groupsets to compare to a lower end groupset but as an inspector of everything from aircraft to medical devices, nuts, bolts, and things from plastic injection miles, castings, machined parts, familiar with welding, plating, materials etc. There could be so many differences not really visible to the eye that could make a groupset much more expensive. A grade 5 bolt looks very much like a grade 8 bolt for example but for certain installations grade 8 bolts are specified.