Yes, the passage you quote from SM is a great example of "If I Ran the Zoo," or, here, begged investigative methodology. Also, it's full of begged questions and erroneous, misleading assertions. For example, it is not true that "no attention was paid to the Book Depository" in the minutes after the shooting. Oswald's encounter with a police officer with a drawn weapon on the second floor refutes that claim. SM seems to suggest--zoo-runningly--that law enforcement should have rushed immediately to the sixth floor because that's where they should have expected to find, according to eyewitness reports, a sniper and/or his weapon. But, as you suggest, Hank, the more cautious, rational approach would be to search carefully from the ground floor up, because the police were looking for a dangerous, armed individual who might (as indeed Oswald, though unarmed, did) flee from the sniper's nest to lower floors.
Note also the inflammatory rhetoric of SM's prose. "Constantly and repeatedly"; the Warren Commission "insists"; "belated and accidental discovery"; "pivotal and potentially disruptive." The rhetoric, without factual support, arraigns both the DPD and the Warren Commission. This type of heightened, febrile rhetoric, repeated incessantly for 54 years, has helped perpetuate popular assumptions that are hard to dispel.