Picasso’s bull drawings were a great example of this as well. It’s like you said, an exercise in compression: https://www.artyfactory.com/art_appreciation/animals_in_art/...
Definitely not realistic though, as you said. Pretty cool that I can easily recognize what someone from 17,000 years ago was trying to depict, though.
Leonardo wa dealing with three dimensional forms, lighting, the interaction of light and materials, etc. It's what makes even the picture in the article look "real". It's got nothing at all to do with what Picasso was doing.
"At this stage, another new head and tail are created to conform to the style and direction of the developing image. Picasso introduces more curves to soften the network of lines that crisscross the creature. Once again he adjusts the line of the back which now begins as wave on the shoulders and flows like a pulse of energy along the length of its body. The two counterbalancing lines discussed in the previous plate are extended down the front and back legs to act like structural supports for the weight of the bull. All three of these lines intersect at a point that suggests the bull's centre of balance. Through the development of these drawings, Picasso is beginning to understand the displacement of weight and balance between the front and rear of the animal."
I agree that Picasso's intention with the bull drawings was mainly to draw a mythological or symbolic looking bull, and then deconstruct it into a more abstract, simple looking bull. He was almost flicking through the range of aperture changes in our symbolic internal representations of things, from finer and crisper to simpler and more abstract.
But I also think part of what informs him and his cubism, his method for dissecting and understanding these ideas, takes greatly into account "three dimensional forms, lighting, the interaction of light and materials, etc" as you like to put it. Unlike Leonardo, he was uninterested in merely making them faithful to reality, instead he was trying to put many instances of reality into one instance, like a prism. I think you are underselling the overlap in their interest about reality and the value in faithfully depicting it. Both are clearly obsessed with it. Even if they both go radically different directions, since of course they lived in different worlds basically.
Perhaps there is something more real in a representation in depth than in a “realistic” image.
https://harvardartmuseums.org/index.php/article/homecoming-f...
https://www.pubhist.com/person/286/edgar-degas/works/drawing...
Sargent knew how to draw:
HN discussion: https://news.ycombinator.com/item?id=7872661