Gladwell's process serves well enough as a lazy caricature for the piece but doesn't represent a good-faith articulation of his subject's views, which is hard to excuse in light of the dozens of events, thousands of tweets, etc. that are much more accessible than Ellsberg material was decades ago.
Gladwell could have interviewed Snowden and Ellsberg but probably chose not to, perhaps because it was easier to trash-talk someone whose life is under threat at an especially sensitive time (pardon consideration) for a "clever" contrast with Ellsberg than to try to represent his perspective in good faith.