Unicode describes flags of nations that no longer exist, dead languages, etc - I don’t see why having a few pictograms that may or may not be relevant in 1000 years time is the place to draw the line. If skin tones play a role in pictographic communication today, then that’s good enough for inclusion.
Put another way: Unicode seeks to describe all human written language. Emojii is unusual in that TUC is actively playing a role in the evolution of the language, but they’re still trying to describe a written language the way people want to use it. This feature sees a lot of use, which to me says that TUC has correctly described how people want to use pictographic communication.