The book of Enoch, from internal evidence - both language and references to other works - is clearly of late authorship, composed some time in the 3rd or 2nd century A.D. The Ethiopian canon is clearly more broad than even the Greek Septuagint. However, they do not claim, nor seek to prove such an early authorship. The point of view of the Ethiopian church is that they honor both scripture and tradition. From http://www.ethiopianorthodox.org/english/canonical/books.html -
The word of God is not contained in the Bible alone, it is to be found in tradition as well. The Sacred Scriptures are the written word of God who is the author of the Old and New Testaments containing nothing but perfect truth in faith and morals. But God’s word is not contained only in them, there is an unwritten word of God also, which we call apostolic tradition. We receive the one and other with equal veneration.
They also clearly accept the late authorship of the book of Enoch:
Among these books is the book of Enoch which throws so much light on Jewish thought on various points during the centuries immediately preceding the Christian era.
The other question here, has there been any attempt to defend or support an early date and authorship? Any attempt to do this is of course ignoring the evidence. Despite that, there is actual evidence that the book of Enoch is preserving a very ancient tradition, that may even go back to the date you suggested. From http://bibeltemplet.net/enoch-southpole.html
Now, over this abyss, where the heavenly fire goes up and down like immense pillars, there are seven stars. This is of course not stars here on earth, but stars hovering over the South Pole horizon. A well known formation of seven stars is the Pleiades. Were the stars Enoch saw the Pleiades? Several things seems to confirm this. Firstly, the angels tells him that certain fallen angels were to be bound to those stars, because of their mingling with women on earth.
This story is very similar to myths in Greece and Mesopotamia. In the Greek myth, seven women were put in the starry heaven because of their mingling with the Titans, by which they were made pregnant. This is also a clear parallel to Genesis 6. And in Enoch, which describes this story in detail, we read, in the chapter after chapter 18, that the women who were seduced by the fallen angels, were to be imprisoned together with those angels, among those seven stars. These Greek women were called the Pleiades, and thereby we know that those seven stars in Enoch must be the Pleiades.
Then there is also a myth from Mesopotamia, where seven demons were bound as seven stars in the sky. Also here those stars are identified as the Pleiades.
So, there seems to be a very old and ancient tradition, which found its way not only in the book of Enoch but also in the myths of Greece as well as an ancient tradition in the Middle East. One may surmise these were probably not "angels" at all but rather a race of extraterrestrials, as the Bible itself states that the offspring became a race of giants that inhabited the land of Canaan, before the Israelites wiped them out.
Sort of now this has become an odd "footnote" of Biblical research that no one wants to talk about - even in the early centuries the Jewish rabbis suppressed this sort of interpretation for the "sons of God" in Genesis 6.