Just had no desire to read further, I started with the impression that there will be some strong arguments against multi monitor setup. May be for the author's needs a single monitor suffices, he earlier had a multi monitor setup, so he ended up using the excess which made him unproductive. That is not a multi monitor setup being useless problem, it is a problem of you not having a use case for multi monitor setup.
Of course if one is using a multi monitor setup to do multi tasking, that is not really recommended. But there are many tasks where a multi monitor setup makes you feel how you lived without one for long? Sample: When I work on an Xcode app, I have one primary 25" monitor fully dedicated to Xcode (IB, editor, inspectors etc) and the second 22" monitor dedicated to Xcode docs, browser with relevant docs/tabs (no email etc), terminal all arranged with Moom. Trying to do this on a 13/15" real estate will make me work at a snail's pace or even negative pace for the constant switching.
>> Deep work is becoming increasingly hard in our distraction
I think Cal Newport must be having a free healthy daily dose of laughter given every Tom is referring to Deep Work when talking about Focus!