I am not sure what your point really is about "..can't drive any
power amp to max output..". "Any"? It certainly can drive many commonly used power amps such as the 200 W Monolith's and many other amps! Regardless, he has no way of knowing what kind of power amps people will use with their AVR, but he provided the graph of SINAD vs output level for up to 2 V, that's pretty typical for most reviewers including Gene who also mentioned that 2 V is what one should aim for, higher is better obviously but 2 V can drive class AB amps that typically have gains around 28 to 30 dB gain to 315 (28 dB gain) to 500 W (30 dB gain) 8 ohms.
If you want to see the SINAD (harmonic distortions and noise) or IMD (intermodulation distortions) in the lower output range, all you have to do is to read the graphs included in his measurements, such as the following:
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