RGB Primaries and Color Balance RGB are doing very different things. RGB Primaries is essentially a simpler channel mixer, while CB RGB is for more “broad strokes” color grading.
Here’s an illustration of what RGB Primaries does:
It’s great for moving colors around and for some creative white balance, but I wouldn’t use it for general saturation and grading, since it only works on the primaries and white point.
And while keeping linearity is good, I wouldn’t get too hung up on it. The developer behind the scene-referred workflow (and CB RGB) has even said that it’s not really that important when working with colors. It’s mostly tones that benefit, and why they should be manipulated early in the pixelpipe, if possible (but again, don’t be too rigid about it).
The CB RGB sliders are really not that crazy, there are just a lot of them. The manual page has a link to the page that explains what the terms mean.