I think for agencies as far as how we appear in organic search ourselves, we are definitely going to need to leverage all 3 of the solutions you talk about and agencies who haven't branded their products/services are going to have to do that and are going to have to also employ branding strategies. In addition, we have to optimize for other search ares like you say in your point #2 and we must look at optimizing existing content for voice search and answers/featured snippets like you say in point #3.
Link building is a catchall term for the practice of creating new external links to your site. Beyond creating great content people want to share, guest blogging and asking webmasters from authoritative sites relevant to your business to link back to your pages are great ways to build links. When possible, use keywords are the anchor text for your links, as this will help send signals to Google that your pages are relevant for those terms.
Although it may have changed slightly since BrightEdge published its report last year, the data still seem to hold true. Organic is simply better for delivering relevant traffic. The only channel that performs better in some capacities is paid search ads, but that is only for conversions, not overall traffic delivery (Paid Search only accounted for 10 percent of overall total traffic).