In photoshop you can easily control the ratios of R, G, B, yellow, cyan and magenta.
For sure, but then you have "false color". As mentioned we can think of an image in 2 parts, luminance and chrominance. An nebula or galaxy etc.. has a certain ratio of color "chrominance". And we then perceive that color based on the relative intensities and sensitivity of our eyes to that color this is "luminance.
So, by definition, an image should have a certain amount of luminance which by definition should match "chrominance" in a specific ratio. In our hobby we modify luminance (and "chromonance") to enhance visualization of features and detail in the image. So, I think we are really generally always working with "false color" images. That is why I don't think there is a strong argument to using RGB to begin with and extracting the luminance (unless you just prefer processing that way, or like the results better).. Unless we only do a linear stretch of the data, equally on all channels (once white balanced), and maintain the luminance in a 3:59:11 ratio, then we really do have false color.
So, there are two benefits to using L i think. If we collect a separate luminance image, this allows us to increase the SNR of the image, as no light is being blocked by the filters for the L. And two, we can work on a luminance image, which is essentially adjusted to remove the limitations of our vision. with respect to sensitivity to and perception of certain colors.
So, yeah, we do sort of end up with a false color image, but I seems that the way we proccess images in the hobby, we do regardless. Also, as mentioned, we are again only really increasing the SNR of the L, not the color, but do we care if it looks better? The L is where the detail is, and the RGB is distorted either ways.... So, to me, I'm perfectly happy distorting it a bit more to sample the detail a bit better.