@trapsarebetter
Drawing manga needs a very different set of skills even if they were still drawing on digital.
e.g. layout out the panels in a meaningful way (can't use 4koma for everything), using tones, strokes, and shading that will go well with black and white print, composing multiple scenes in a meaningful sequence, backgrounds - whether it be using photos, using a 3D program, or drawing it manually, etc.
@trapsarebetter
Yeah, that's the weird part. It's just that usually, the manga artist is different from the light novel illustrator. However, Arumi as far as we've been shown is also another light novel illustrator.
Both Sagiri and Masamune are literally kids, so they wouldn't know about these stuff. At the moment, they only set up these requirements: illustrations that can rival Sagiri, loves their novel as much as Sagiri does. Sure, Arumi fits the criteria, but it seems that they forgot that they also have to be a manga artist.
@jonsmthNo Game No Life was actually illustrated by the writer, who then collaborated with another illustrator on the strip, who was also the illustrator that took over the book, for a while, when the original artist was sick, whom the original artist is also married to.