I think there are a lot cannabis growers who would disagree with you, Daisy, about the grow lights that have more emitters in the red and blue spectrum than compared to the full spectrum or other wavelengths, not being useful/better for plants.
You make the point yourself to some extent: it is a fact that wavelengths in the 425-450 nm (blue) and in the 600-700 nm (orange-red) are most efficiently used for the major aspects of photosynthesis by plants, that does not mean that the remaining wavelengths are useless and therefore not necessary, but what you see with a lot of the LED grow lights is that they have a larger number of red and blue emitters than full spectrum emitters. I have a couple of LED grow light bars where for every full spectrum emitter it has 2 blue emitters and 3 red emitters giving the overall light coming from them a blue-ish-red glow which, if I would have it on it the daily living spaces of the house, would be irritating and tiring for the eyes, though the plants certainly would not mind.
I think how you should express the warning about red/blue wavelength grow lights is that you should never get a light that is just red or blue emitters, but getting a light bulb/bar that favors red and blue over full spectrum to some extent certainly is not bad for the plants, especially if that is to some extent supplemented by natural light. In the same way that some fertilizers come with more of a specific nutrient over another because it is known to be slightly more important or needed in higher concentration.
