I don’t know if Leonardo or Rembrandt were realists - I’m not sure the term was ever known in their lifetime. What you mean is that you can see immediately what they are portraying. That is sometimes labelled as naturalism although that term wouldn’t be known by them either. This is what people hated about the impressionists - you couldn’t always tell what they were representing. Today, of course, people who know nothing about art can appreciate them. Their eye has become used to seeing.
Davinci always had an elaborate scene behind the subject and he paid extra detail to curtains and cloth. Incredible! The Annunciation is one of my favorites.