This is a rather disingenuous statement to say the least !! As with the other Canon off sensor ADC cameras if you want the maximum quality that the sensor can bring it's important to nail the exposure, and if you do this then the 5DS/r has excellent shadow recovery and remarkable highlight recovery, certainly more than you can ever fit into the DR of a print or even high quality screen without looking ridiculous. I know some people have associated the shot noise (photon noise) of the 5DS as "poor quality" but this is just normal physics and you see the same in any very high mp / small pixel / large output sensor.I am speaking this as a 5DS R user for the past 6 years. 5DS R is a package with tons of pixels but no sensor performance.
The meter on the 5DS is very good but even then I still use an incident light meter when practical.