I’m not sure what you’re getting at, but to satisfy your curiosity, those animators have been drawing for years now. Before having all those mileage, they absolutely needed block out all major forms and line up perspective, like us babies.
The reason why people like Kim Jung Gi draws the way he does is not because he is a genius who was just blessed with remarkable visual memory. It was because he studied all those fundamentals, perspective, proportion, line quality, etc. He drew so many times from reference that he doesn’t need it anymore. Same thing with those pro animators, they’ve drawn so many scenes, observed and studied so many references that they don’t need them anymore.
If you look at Bahi JD’s tumblr, you’ll notice that he does box out his characters in some of his rough animations’ posts. Who knows how much practice he’s done behind the scenes, even if someone frequently uploads their art, the ones published in social media must be the pretty ones, no matter how transparent they try to be.
Again, I’m not sure what you are trying to achieve with this question, but to give advice for anyone that is reading is to lower your ego and study those fundamentals. Draw cubes, cylinders, spheres that will become the cornerstone of dynamic poses in perspective. Eventually, you will get there. I promise. There’s more good news, all of you have access to what those old japs animators don’t have, the ability to browse through the internet and access all of the limitless references. Imagine if Leonardo Da Vinci had an iPad.