The figures (150 verbal IQ, etc.) seem to be plucked out of thin air, and the central idea---that there would be an IQ 'threshold' separating people who can be successful/good writers from those who can't---similarly backed by nothing. Where is even a hint of what a mechanism for such a threshold might be?
Trying to show off how smart one is is probably part of the motivation behind many interesting comments posted on here, and more generally, a big motivation behind a huge number of the useful things people do. Doing it in a non-obvious way requires additional ingenuity. The cumulative effect of people trying to show off how smart they are has undoubtedly greatly accelerated the development of our species.