Do you guys know The Oatmeal? It's a website with mostly comics. The stuff is good and that's why people visit it, but what's amazing is this: according to SEMRush, it's ranking for 3500+ keywords! And we're talking about a website that ranks for general high search volume keywords like "literally" and "semicolon" with a landing page that doesn't have that word anywhere on it. What does that tell us about on-page optimization? Clearly, it's not as important as we think, huh? While most of us worry about keyword density, word counts, LSI usage and all that, The Oatmeal doesn't give a damn and it's ranking for 3500+ keywords.
Okay, let's entertain the thought. Okay who is actively trying to rank for "semicolon" or "literally"? Additionally let's entertain the fact their site is aged and has PR of 6! Their offsite authority is rather high and Google will immediately place their posts ahead due to this. Onsite: Notice how when you search for Literally the Displayed text is Optimized for the keyword? They do their major Onsite SEO with the search engine's description & title of the page. All images have an appropriate Alt tag. Anyways: Believe what you want to believe. As google increasingly devalues link types onsite seo is beginning to be a prominent factor in ranking alongside of domain authority.
If "major onsite SEO" is as simple as that, then why do we have to care about the other factors? That's the point of this thread. The Oatmeal has powerful off-page optimization and that is seemingly enough for it to crush a few hundred million websites in SERPs. Maybe off-page is all we need? Let's see you try to rank for a keyword like "semicolon" and "literally" if that's easy.