The thinner description still isn't making any sense.
What it seems like you are trying to say is that each stop of extra exposure adds less density than the one prior, essentially the separation of tones gets smaller and smaller as exposure increases.
If true, this would mean less detail is available in the highlight areas. If true it would also seem that Kodak's curves are wrong, i.e. The straight line should actually be curved.
Across a single negative in a shot of say a wedding party the bride's dress could never show as much detail as the groom's tux. The bride's chocolate Lab would have better color separation than the Bridesmaid's light blue dresses.
I did a test a while back. Several 5-shot/stop bracketed sets of 35mm 160nc film.
Contact printed them.
Across a single scanned contact print the color balance remained constant.
I printed several versions varying only enlarger exposure to place one common neutral tone at the same point on paper and it was pretty darn easy to make the variously exposed frames match nicely.
Admittedly this wasn't a rigorous lab study but I was carefull to do things carefully and used PS to measure the resulting print scans.
I found no practical difference in detail or color at the main subject.