Kevin Gibbons, something of a player in the UK SEO industry, ran a Twitter poll in April this year on the key features of SEO. While the true answer might be nearer to 'it depends', as noted by a couple of respondents, the breakdown is nonetheless illuminating. 

His followers are from across digital marketing. Of the 1,400 or so votes, 59% voted for the primacy of on-site content. A resounding result. 

As a platform that is designed to enable professional services to have up-to-the-minute, expert-led on-site content and provide 'technical SEO' as a given, this is great to hear.