Rosy / mauve is for pale / fair skin not medium skin tones it doesnt look good on that it doesnt look good on tanned skin .It would wash you out.
You clearly have some strong opinions, but I perceive you to have an "it's all or nothing!" mindset. All cosmetic lines have their stars and their duds and certainly not a one size fits all. I love some things that others dislike and vice versa. Hate MAC all you want - just means more for us. But there's an undertone of beratement for others who do enjoy the brand that's uncalled for.
I think a flat out blanket statement such as the one you made above are inaccurate. It's like saying light beige/nude shades will never work for deeper skin tones. It's a crock of shit, because I see ladies here on Specktra with deeper skin tones that can rock the hell out of nude lippie, that I personally can not, but I know better than say that no WOC could do it. Like erine1881 said about, it's about finding the right colour, shade, range, etc. It can be done it just come down to whether you want to explore it for yourself.