Alright here's Golden's response:
He then sent voice notes (I had dm'd him on telegram) so bear with me as I translate his thoughts:
He clarified that what you said isn't necessarily wrong but that it is assuming that a tube or transistor is going to behave identically in all situations, which they won't.
Solid state devices typically perform more linearly--- so usually you don't see this behavior on them.
But tube devices, in his experience of testing them, generally perform better with a lower line level input voltage, so that's why he recommends at least trying it to see if it improves your subjective experience. He said this is because they are not perfect devices and they don't perform linearly in all situations.
He also said you are correct about increasing the noise by turning up the volume on the amp, but that noise and distortion are separate issues that are effected differently.
He basically said only put the volume as loud as you can without hearing noise, if you hear noise turn the amp down and dac up.
He said if you can do this without getting a problematic noise floor at the output, it's probably worth doing. If your amp is noisier and you get a ton of noise by doing this, then it's not worth doing. The aegis is a quiet tube amp so I feel like it's worth giving it a shot?
There are far too many unknown variables in those measurements for me to draw any conclusions. What I will say though is that any amp, tube or solid state, that is generating 1.4% THD at 700mVrms output into any load is poorly designed.