Safari does use your bookmarks and your history, but at some point the history expires so some sites I go to rarely don’t autocomplete and I add bookmarks when I notice.

Also it sometimes is too slow to pick up that I don’t want to go where it autocompleted, I hit go, then immediately hit back and typed more characters in to get the actual site I wanted. I could go and edit my history, but that process is a little clunky on my phone.