Obviously a superior format has to be graded with higher standards. I agree the reviewer can't fully appreciate the benefit of the format because an important (well, THE most important) component is lacking, but there are many others out there without HDR displays that can fully appreciate his...
I don't know that's seems about right. If the UHD can't even beat the Blu-ray that's probably the most it deserves. Do you think a Blu-ray could possible get more than 3 stars if it were DVD quality?
The HDR actually increases the level of visible detail. There is a lot of light-based detail that is obscured when the 2k master is 'dumbed down' to SDR home video. That said, although HDR is the star of the show, I have enjoyed the resolution upgrade on a few titles, notably Expendables 3...