Why would the use of the phrase "in two natures" be a problem. It is what is mean by any language that is always the issue.
I agree (of course). I think it's also worth noting that the book is addressed to Leo, who was a deacon in Rome at the time. It was on the basis of this book that Leo urged Pope Celestine to condemn Nestorius- the other major factor being, of course, Cyril's testimony. I point this out only because I get the impression that some think the phrase "in two natures" used at Chalcedon was simply a borrowing from Theodore of Mopsuestia or his school, when actually it was just a translation from the Tome of Leo, who in turn was taking this language from John Cassian's book against Nestorius.
Ya, I think the main problem is communication. Because of "guilt by association", we never got a chance to study the Latin tradition of the use of the phrase.
In all intents and purposes though, St. John Cassian is venerated by us for his spiritual works and his connection to the Egyptian desert. I am not sure his Christological works was well known. St. Severus of Antioch's list of fathers included St. Irenaeus, St. Athanasius, the Cappadocians, St. John Chrysostom, and of course, St. Cyril. It seems like St. John Cassian was not really heard of as much.
