Frankly, I would not take anything Arnie said seriously and would toss his book in the trash, where his "music" belongs as well. Perhaps set fire to it.
It is also blatantly false when he says that "No beginner is capable of envisaging a composition in its entirety". Of course they can. Even laypeople can. They are capable of "envisaging" it, but that is different from "realizing" it entirely.
The truth is that even if you plan out a structure or form from the get go, pieces tend to undergo metamorphosis as you actually work on them. The music reveals things to you that may not have come to you while you "envisaged" it and every piece is different. On some, you might have thought of a form you want beforehand and you wind up following it exactly. On others, you might realize partway through that actually, it would better if this "B" section didn't repeat after all and you have a better idea.
And yes, it can even unfurl like a tapestry on a one-note-to-the-next basis.
As an example, on my last album, some pieces I had a very clear picture of how they would be laid out before I even sat down to work on them. But on others, I did not.
On one track I wrote, all I knew for certain was that I wanted it to start with some soft horns, and end with a big march that fades out into percussion similar to "The Flag Parade" by John Williams. I wound up having to change the ending because the company I wrote the album for required every track to end on a hit, but everything between the intro and ending was up in the air.
It wound being the most popular and best-selling piece on the album — and is also my favorite piece on it.