I mean, you take one look at Greek statues and Roman busts and you realize that people figured how to aim for realism, at least when it came to the human body and faces, over 2000 years ago.
Yet, unlike sculpture, paintings and drawings remained, uh, “immature” for centuries afterwards (to my limited knowledge, it was the Italian Renaissance that started making realistic paintings). Why?
Realism wasn’t necessarily the end goal of a lot of painting. When you look at old Christian art one thing to notice is that different people can have vastly different sizes. The virgin mother may be most prominent, some patron saint smaller, and the artist themselves or the commissioner may be included as smaller figures. This play of scale was a device to show what was important and being sure to capture and portray that hierarchy was a more important goal than realism.