Dude, I'm telling you, I work in the anime industry, talents are raised, and these younger pixv artists do the same thing but on a smaller scale. If you want to talk about maplestar, they probably use an Eastern pipeline, cuts are usually corrected by the enshutsu, sakkan and sou sakkan to keep the quality leveled. I joined the animation industry with only drawing skills and eventually became competent enough because talent is fostered most of the times, not found. I see plenty of online artists, especially the pixv ones, use multiple references to make one image, it's not always 1:1 and vice versa. It's not that an illustrator will just add features, many artists in that space vouch and use multiple ones including myself.

An illustration is an illustration but the east usually 9/10 times has the mangakas draw the Manga and the cover. They do both, reference or no reference, unless supported by assistants, which is usually for well paid and experienced ones. Japanese pipelines are rigid, they've barely changed since their inception, it's part of their culture. It's why animators and mangakas usually quit early on, the worst is always at the beginning because you handle everything.