...Not sure if serious :|You do realize that Itachi speaks Itachinese right... so basically he seriously does mean that ama/Tsukuyomi is required to awaken Susanoo as it is just something that is "rarely" awakened as only 3 Uchiha have only been seen to have been used... two of whom btw have both Amaterasu and Tsukuyomi and we have not really seen all of Madaras movesets anyway
Yes, they behave similarly but they arent the same. Tsukuyomi is a powerful genjutsu that allows the user to manipulate the genjutsu in any way he sees fit. Madara did the same thing to obito however he used a regular sharingan genjutsu. This means that the gedo mazou's chakra allowed madara to perform a more powerful genjutsu, but it was not a mangekyou dojutsu.That is actually a fair response. However, at the time, Tsukiyomi didn't have a name- and what he described is almost exactly what Itachi told Kakashi in part one.
So Itachi has tsukuyomi, an MS dojutsu which allows the manipulation of one's own genjutsu. & madara has a regular 3-T sharingan genjutsu, powered by the mazous chakra. They both do similar things, have similar names, but they are different.