It's very interesting to see how much writing Gene Roddenberry did on the series, conforming the scripts from others to his vision of the series. While plenty of others contributed much, Roddenberry was far from the "do nothing credit hog" people have been making him out to be. Also, at the time, Shatner was considered an amazing catch, a major talent on the rise who just needed the right series to propel him to stardom. The respect he commanded was considerable.
Man... Star Trek a ratings winner? Roddenberry busting his back on the series? Shatner a great actor? This book has made it opposite day!
As an aside, the back cover copy also claims that the episode "Sarek" (for which Cushman received co-story credit) was "the first episode of [TNG] to include a character from TOS and thereby link the two series together." This is a bizarre claim to make considering that DeForest Kelley appears in "Encounter at Farpoint" and Kirk's Enterprise (and the plot of "The Naked Time") are referenced in "The Naked Now," the following episode.
Well, to stretch it a little, McCoy was not named in the episode as anything but "The Admiral." And none of the original series character actually appeared in The Naked Now, but I agree, these links were there. However, "Sarek" was considered the first episode to truly acknowledge the original series by the Piller and Berman and the folks in charge going forward. But that sounds less impressive in a book