Just drawing requires actual skill, it's easier when you either don't care about it being consistent and good or when you're up there with skill that you are effortlesy consistent and good. Posing and tracing is easier if your skill is lacking and you’re trying to pretend you're better than you actually are.
I doubt the artist would pose the dolls themselves, often those manhwas have nameless helpers doing the dung bettle work.
Tracing the 3d dolls is easy when you know what you're looking for- clip studio heads have very distinctive sculpt, also the bodies are often weirdly stiff when the perspective and poses are extravagant.
Those dolls are great visual help tho, when the pose is weird - but the artist needs to be really good to not make them look like traces.

Why do I feel like the author of this story wasn’t satisfied with bye-bye story which was so wholesome so she made a different toxic version, which is this ass story. Like I would like to rate it a zero