The idea of using Itachi's feat to account for Madara's is not proof. People use this defense to make sense of the issue, but it doesn't explain it at all.
Itachi using Susanoo while nearly blind is completely different than using it without eyes. Itachi may have still had his MS activated but we couldn't see it. In that situation, showing Itachi's descent into blindness took precedence. So no, this panel of Itachi proves nothing because he may have still had MS activated and Kishi instead wanted to make it clear he was going blind, thus the visual of his MS was trumped.
Madara using Susanoo without eyes is on a whole different level. I'm not arguing against Susanoo being a manifestation of chakra, I'm arguing that only Madara achieved such a crazy feat and not Itachi.