That is a matter of opinion. There are assumptions made about Daniel’s writings too, but he accurately prophesied the march of world powers from Babylon, right down to the present day, all of which had dealings with Israel. (Described in the Bible as “the Gentile Times” or an historical period where the Jewish nation would have no king, and be ruled by Gentile nations.) When Jesus walked the earth, Rome was dominating the Jewish nation. (Daniel ch 2)
“Though some have pointed to the book’s change of style from
chapter 40 onward as indicating a different writer, or “Second Isaiah,” the change in subject matter should be sufficient to explain this. There is much evidence that Isaiah wrote the entire book that bears his name.”
The Dead Sea Scrolls, included the prophecy of Isaiah.
“This well-preserved pre-Masoretic Hebrew and is some 2,000 years old, from the end of the second century B.C.E. Its text is thus about a thousand years older than the oldest existing manuscript of the Masoretic text, on which modern translations of the Hebrew Scriptures are based. There are some minor variations of spelling and some differences in grammatical construction, but it does not vary doctrinally from the Masoretic text. . . . these ancient scrolls refute the critics’ claims of two “Isaiahs,” since
chapter 40 begins on the last line of the column of writing containing
chapter 39, the opening sentence being completed in the next column. Thus, the copyist was obviously unaware of any supposed change in writer or of any division in the book at this point.
There is abundant proof of the authenticity of Isaiah’s book. Aside from Moses, no other prophet is more often quoted by the Christian Bible writers. There is likewise a wealth of historical and archaeological evidence that proves it genuine, such as the historical records of the Assyrian monarchs, including Sennacherib’s hexagonal prism on which he gives his own account of the siege of Jerusalem.
*(
Isa., chaps. 36, 37) The heap of ruins that was once Babylon still bears witness to the fulfillment of
Isaiah 13:17-22.
* There was a living testimony in each one of the thousands of Jews that marched back from Babylon, freed by a king whose name, Cyrus, had been penned by Isaiah nearly 200 years earlier. —
Isa. 44:28; 45:1;Ezra 1:1-3.”
Excerpts from
Bible Book Number 23—Isaiah — Watchtower ONLINE LIBRARY