On-page SEO?

One can rank 1st on low competition keywords with on-page SEO alone.

Slowly but surely that approach builds up enough natural backlinks and overall authority for Google to rank such a site even for the more competitive keywords. Talking from experience. I've overtaken niche authorities like this, forcing them to resort to copying my content and employ other SEO tricks in order to not lose it all... Ever since figuring out this game I haven't bothered building backlinks because if I did I wouldn't know if I was building the right content for the audience and might never outrank the leaders in a given niche. That's to say, in my opinion, on-page is more important than off-page when it comes to the long game.

On page SEO is where optimization begins. Highly influential factors for user experience like bounce rate and well-structured posts.

The On-Page is a very essential part in the SEO .Because if there is no onpage then nothing which includes Keyword Research ,
Meta tags,description ,content and so on ..

That is a very broad question! What exactly are you alluding to? It is an important strategy in SEO. One that shouldn’t be ignored if you want to rank for your keywords on title properly.