Here are my guidance about Digital Marketing (I take from a dead good site named digitalmarketingcalculator.com from 2013):
1. Content Marketing
2. PPC
3. SEO (may be they mean offpage-SEO, cause on the point 1 we have saw Content Marketing where is On-page SEO is a legacy)
4. Social Media Marketing
5. Video Marketing
6. Email Marketing
7. Mobile Marketing
All newer digital marketing calculator are too sporadist in calculate anything without integration between one and another points.
But, still I'm solely sure that traffic is better than baclink from whatever link building we did. You are right that on-page seo and off-page SEO have to working together at the first time you starting your porjects, but than traffic will be the ultimate one you need. We can build any backlink, but if no visitor come to our site via any channel we have done, we will kick off by the clients.
Traffic, organic traffic, from real human or just fake visitor, are very very important point from here.