The bottom line is, no one would ever have thought that two writing styles for two different topics in one book, Isaiah (that has historically always been recognized as one book, going back to 200 BC in the Septuagint), had to have multiple authors unless it predicted events in detail over a century in advance.
Again, you are attempting to tell people what they think while ignoring many other books of the Bible where the same textual analysis has revealed multiple authors and sources or that the books and passages could not possibly have been written by who they claim to have been written by when they were supposed to have been written.
You are making false claims about what scholars think when all you have to do is read what they have written to know what they think and why.
Also, there are several serious issues with chronology in the book of Isaiah. The first 39 chapters speak of the destruction as imminent. The second section speaks of it has having happened and restoration of Israel as a future event. The third section speaks of the restoration has having happened. Why would a person writing prophecy speak of it all in three different contextual time frames, will happened, happening now and has happened? If your model is to be believed, it was all future events, so why the change in mentioning yourself, writing style and tense?