Ok I don't know him. And as a PR guy it's no surprise I'd jump to the same conclusion. But he makes a good case not just for the PR agency to lead, but for why integrated teams across different kinds of agencies look better on PowerPoint than in reality.
Brands need their agencies to play nicely and put the work over and above their individual financial needs (and egos), and the best PR firms work flexibly in all kinds of arrangements.
But the next time you're assigning responsibility for social media management, think twice taking the 'committee approach' or assuming it should go to your ad or SEO agency. If your PR agency has resources for analytics, paid amplification and content production - which they should - you may have everything you need right in front of you.
fore, I strongly believe that the best agency to own social media is today's PR agency 2.0. PR agencies are already set up to facilitate and ignite conversations between brands and consumers and with some multi-discipline support, can be a social media dream team.