Good points, thinker. I wanted to widen the context along the lines of peacefulpete's comments:
There is no evidence that any Hebrew or Aramaic writer ever used the term "watcher" to refer to angels until the Hellenistic/Maccabean period. Daniel is the one exception, because Daniel was supposedly written in the 607-537BCE period and he also called angels, watchers. Of course, there are about 30 other lines of reasoning that show that Daniel was written in the Hellenistic/Maccabean period, probably around 190BCE. It seems that this is the opinion of almost all non-religious scholars and perhaps, by now, most religious scholars, too. (I first learned it from the Catholic Jerusalem Bible footnotes.)
Daniel, according to most scholars, belongs to an important group of "Biblical" (but not canonical) writings known as the pseudepigrapha. (It's like "apocrypha," but also written under an assumed name of a former hero like Noah, Enoch, Daniel, Solomon, Elijah, Moses, Abraham.) There are therefore many would-be Bible books written around the second century BCE that bear the names these "authors" even though those authors had obviously died hundreds of years earlier. To be fair, most of the OT and much of the NT canon contains many books whose authors were anonymous, but which were later assigned an "appropriate" author, like Psalms, Proverbs, Song of Solomon, Ecclesiastes, Matthew, Mark, Luke, John, The Five Books of Moses, etc. These are not in the same category because the text of Matthew, Mark, Luke and John, for example, never itself claims that these men were the authors. Revelation does claim to be written down by a person named John, but is obviously not related (linguistically) to the writer of the Gospel and the letters attributed to John.
I know a lot of people already believe all that, but I repeat it because it's in combination with some of those other books of the Hellenistic/Maccabean period that we can get some further understanding of what Daniel was referring to by watchers and archangels.
For example: 1 Enoch called angels "watchers" so often that chapters 1-36 are referred to as "The Book of Watchers." Then there's Daniel with a similar view of angels as found in Enoch along with the same expression for angels in Daniel 4:13,23, for example. It's especially the fallen angels referred to as watchers, and these are sometimes considered to have been from the same group who were assigned to watch over humans, with arch-angels watching over the watchers, on a nation-by-nation basis. You can also see this idea in: Testaments of the Twelve Patriarchs (5:6). Jubilees 4:15, 21-23; 7:21-23; 8:3; and 10:5. "Testament of Naphtali" (3:5). All of those books come from the 2nd Century BCE.
Jude, in the NT, 1st Century CE, refers to Michael disputing with Satan over Moses' body. This comes from the apocryphal book The Assumption of Moses. (In another book, The Revelation of Moses, Michael also guards the body of Eve.) The book of Enoch, like Revelation 12, also has Michael and Satan battling over the fate of Israel. (Satan/Samael is Israel's accuser and Michael is Isreal's advocate (just as in Daniel, where Michael is Israel's angelic prince and some unnamed angel is Persia's angelic prince.).
JWs are not the only religion to try to turn Israel's arch-watcher into Jesus. I agree that "thinker" shows it is impossible to say this strictly from the "literature" of the time. But anything is possible when you wrench it completely out of context, and only read the Bible while on the lookout for proof-texts. It's a little easier to see what these writers had in mind when we see that the apocrypha and pseudepigrapha were still important to them, which is why they are at least indirectly referenced by "Daniel," Paul, Jude and John (Revelation).