How can the manga artist be so bad at understanding the basics of traditional art? That shouldn't be possible at his skill level.
I mean, any traditional artist who focuses on portraying people is bound to often use charcoal and ink, because paints are both expensive and not efficient for learning figure drawing. Mastering ink is not a big deal, so there is no need to wait for someone to bring artwork specially made with ink.
Besides, as an editor, MC's approach to scouting artists is terrible and unprofessional. Everyone should be given an equal opportunity, so he should start by putting everyone on an equal footing by giving everyone a test task and the same set of tools. Rejecting the court artist who offers his help is nothing but blind arrogance.
I bet this is the manga artist projecting his own views by looking at how the manga is drawn with ink. It seems like he really believes that his ability to work with ink is somehow more important than anatomy and composition.