>The keyword here, though, is reproduction. A printer isn't capable of mixing pigments the same way an artist mixes paints on a palette.

This is kinda no longer true. Computer tools such as “krita” (open source) do an exceptional job emulating paints and brushes. A lot of professional illustrations now days are done digitally and printed. “Art” less so but the tablets keep getting better.

https://krita.org/en/

As someone who was kinda adept at making black and white prints from negatives, I kind of miss some of the old tech (making prints was a little magical). But digital / ink jet can get you 90% of the darkroom much easier and has some serious advantages.

I do applaud the effort and the fun factor here is real. Those pen plotters are neat and enough different to make this an interesting niche.