I wouldn't say no one uses the unnatural skin tones like a few have mentioned Berry sims are very popular more so during sims 3 as we had all sorts of colors available to us without CC. The different colors were really handy for supernatural sims like genie's, faerie's, mermaid's, etc. I myself love berry sims and use CC skin to get more colors but sometime's if i play a save without CC I use Alien's for my sims different colored skin tones. Also, unnatural skintones are used sometimes by those of us who like doing the perfect genetics challenge.
So I would look up berry sims and look into perfect genetic challenges and show them to that person who claims there not needed cause i'd say at least half of us simmers use the unnatural skintones in our gameplay.
I even think sims 4 could use more unnatural skintones cause so far only aliens have a good variety of different colors. I think as it stand for non-alien sims we have red, blue, and green.