like it was stated, Tsukiyomi is Itachi's only real defence, and it's flawed really, as we stated, each tendo is like a seperate person, Tsukiyomi isn't capable of catching multiple ppl at once I believe, and once a tendo is in Tsukiyomi, it'll only experience some minor discomfort for a second, and then he'll be back into the fray, remember when Jaraiya caught the 3 pains in a genjutsu, only the bodies were imprisoned, Nagato was unaffected.
Another thing is that Itachi can only use his MS abilities for so long before the jutsu blinds him, and there is no way Susanoo can protect Itachi if the very footing on which he stands is destroyed around him, Susanoo's yata mirror can't save the landscape around him from being destroyed, it's like me expecting bullet proof glass to save me from an earthquake