I think the point that SDR inputs (to a monitor) can be _similar_ to HDR input to monitors that have high dynamic ranges is obvious if you look at the maths involved. Higher dynamic gives you more precision in the information, you can choose to do what you want with it : higher maximum luminosity, better blacks with less noise, more details in the middle etc.
Of course we should also see "HDR" as a social movement, a new way to communicate between engineers, manufacturers and consumers, it's not "only" a math conversion formula.
I believe we could focus first on comparing SDR and HDR black and white images, to see how higher dynamic range only in the luminosity is in itself very interesting to experience
But in the beginning he is saying the images look similar on both monitors. Surely we could find counter examples and that only applies to his cinema stills ? If he can show this is true for all images then indeed he can show that "SDR input to a HDR monitor" is good enough for all human vision. I'm not sure this is true, as I do psychedelic animation I like to use all the gamut of colors I have at my hand and I don't care about representing scenes from the real world, I just want maximum color p0rn to feed my acid brain : 30 bits per pixels surely improve that, as well as wider color gamut / new LEDs wavelengths not used before