what counts as on page optimization?

everything on the page itself that you control. title tag, h1 and subheadings, the actual text answering what the searcher wanted, internal links to and from the page, image alt text, the url, page speed, and the meta description. the other two buckets are off-page (links from other sites) and technical (can google crawl and index it). on-page matters MORE at small scale, not less, because it's the only part that costs nothing but time.