Have you researched the original reason why the "Two-Isaiah" theory originated?
It was because the skeptic could not believe that a detailed prophecy was written in advance.
That's actually not it at all. It's mainly that in some portions, Isaiah talks about himself quite a bit, then suddenly disappears from the text. At the same line of demarcation for that change, God also changes from a god seeking vengeance to a god of love and mercy. Also, after chapter 39, the writing style changes twice, once in the portion of returning home and secondly in the portion after they have returned him.
Finally, the Talmud claims that King Hezekiah wrote Isaiah.
So, next time you decide to tell "skeptics" what they think, you may not wish to confuse "skeptic" with "scholar" and actually have taken the time to read what they have written that will tell you what they actually think rather than make up something 100% inaccurate.