It shouldn't be a surprise that these would be the findings of post-hoc research done in 2021, long after skin-tone modifiers were made available and in common use, rather than research that was done before skin-tone modifiers were added to the standard, so as to justify the additional complexity and possible nth-order societal effects of adding them—which, as far as I can tell, does not exist.

Instead, someone somewhere made the call that giving up the universality of cartoon yellow emoji was worth “making some people ‘feel more represented’”, even despite the numerous other tradeoffs and nth-order effects (no reddish Native American tone, added social complexity for biracial users (“am I ‘black enough’ to use the darkest one, in a given arbitrary social context?”), and so on), which people conveniently ignore.