Is SEO still worth investing in for small websites?

I’ve been looking into different ways small websites can compete with much larger companies in Google, and SEO still seems to be one of the few channels where budget is not the only deciding factor.

Good content and proper technical optimization obviously matter, but backlinks still seem to make a significant difference, especially in competitive niches. The difficult part is finding websites that are actually relevant and worth getting a link from rather than simply collecting as many links as possible.

I recently came across Tier1.shop, which provides access to different link placement opportunities. What I find more interesting, though, is the broader question of whether businesses should actively build links or concentrate almost entirely on content and let links appear naturally.

For anyone here who manages a website or online business: have you seen measurable results from link building during the last year, or has content quality become much more important in your experience?