Here are a few very quick sketches done by my teacher Samuel Kudish back in late 1940s. Dont judge them harshly, he was basically a kid, in his twenties. This was during the War, he got recruited into the army and he drew like crazy every waking moment. This was before he got into Mukhina.
These are fellow soldiers, so I'd say these are 10-15 minutes sketches, at most.
No construction lines here, no see through or anything like this.
He was naturally talented (great sense of proportions, natural organic form and etc.).
However, the way he teaches now his American students is a lot of spheres and cilindars, and their work does look mechanical. He always explains it by the lack of talent, saying that it's the only way to teach someone who does not see naturally.
And, the more talented his students are, the less robotic their drawings look and vice versa.