I think the hackery's necessary in that it's necessary in order for him to have completed his books with as little effort as he did. Writing as well without the hackery would require coming up with better theses (which would mean jettisoning weak ones when you realize they're weak, and starting over, rather than plowing ahead regardless—this could be a long process) and a lot more time finding and evaluating evidence.
Good writing ability (for certain definitions of "good") plus hackery are necessary if you want to make the economics of your writing work as well as he has, writing airport nonfiction books. Writing non-hacky nonfiction is takes a lot more time and (perhaps) more talent.
It's just not the case that Gladwell is only effective when he's teflon-coating vapid, big-sounding ideas to shoot into his readers brains.