Thanks @Elle for the compliment on my painting. I really do need to fit more of that into my schedule 
I do think the Abney effect is a significant part of the “problem”. I tried to recreate the color chart on the wikipedia page but with subtractive spectrally mixed colors. The Abney effect is almost entirely avoided for some reason:
Here’s a side-by-side example of white on sRGB Blue. Same brush, same exact settings, weighted geometric mean mixing, linear light, etc. The only difference is the one on the left is 36 spectral and the one on the right is 3 RGB:
If you’re thinking, “ok, maybe just using wide band spectral is really all there is to this”, that’s not quite entirely true either. Here is the exact same brush again as the first (above, left), but instead of subtractive this is the normal additive mean. Still spectral though:
So we get the full Abney effect regardless of full spectrum versus 3 narrow bands, but really only with linear mixing models, and of course the wiki article only talks about “adding” white light. …