If CEOs were as replaceable and disconnected from the outcome of a business as the author suggests, boards would've started doing this long ago and CEO salaries would come down as a result (lots of people want to be CEOs, and by this author's logic, virtually anyone can do it). This is so disconnected from reality it reads like satire.
You are assuming here that boards are always acting in the best interest of the share holders. I bet there are many who do, but there are at least as many that act primarily in the interest of themselves. Board membership is a lucrative job without much supervision, if any at all. So nothing is keeping board members from taking it easy. Why rock the boat if this can make you known as difficult? You might not get that 2nd or 3rd board membership then anymore.
You might remember Credit Suisse, the major bank that had to be taken over recently by UBS to avoid bankruptcy: until then it had gone from scandal to scandal for 15 years in a row. 2 CEO's had been sent away in that period (by shareholders) but the president of the board? He could stay, and with him the rest of the board. His salary? 7 million a year.