Earlier quoted context omitted.
Asking whether they "swung" the election is an unnecessarily high bar. The question is whether they influenced the election, and the answer is a pretty clear yes. Russian hacks of the DNC and John Podesta, and the ensuing leaks, drove front-page headlines and cable news coverage for weeks in aggregate, if not more.
So is it the Russians or the media reaction that made the difference? If I recall correctly one of Greenwald's main theses is that click-thirsty coverage of exciting-sounding stories overwhelmed more substantial topics in the 2016 election.
So, I agree with Greenwald that a broken media environment made it possible. But I disagree with him that that casts doubt on Russian involvement, or invalidates Russian activity as a topic of national concern.