RGB color cubes use the color space poorly. That's why the Nintendo NES looked better with 54 colors than a 256 color space organized as a cube.

I would disagree, IMO it depends on your level of color understanding and your application entirely.

I've seen people do wonderful things with four colors only.

Exactly. The "web-safe" color cube used on the 1998 web was designed by a physicist. The color palette used on the 1983 NES was designed by somebody who had a high level of color understanding.

If you split up the rgb cube evenly you wind up with many shades of green that are somewhere between "makes me want to puke" and "this is what you see when you get hit with a green laser pointer."

I don't disagree.

That was misunderstanding the application, for sure.

Here is what a physicist would probably do to test that 3x3x3 thing: https://imgur.com/gallery/6HOORem