I remember when alternative music was the new kid on the block, or more appropriately, the new genre. Of course, at the time most of the acts falling into alternative were new acts, who really were doing something distinctly different from the other stuff on the radio. (Yes, this does mean probably lots of people had been doing that stuff not on the radio for quite some time, and the naming of the genre was just some bigwigs at the music companies figuring out how to monetize it.) But then you get far along enough in the game that the new people coming in, grew up hearing that stuff on the radio, they don't enough know what it used to be like, you guys. And you start to wonder, why do we call this alternative anyway, alternative to what?
I think we're getting there with diverse, and getting there with things like own voices. Partly it's just the nature of words, they evolve, or the group being labelled with that word evolves. Code Switch did a story about the predominately white historically black college in West Virginia. So, when we call books that feature characters of color and/or LGBTQ characters and/or disabled characters diverse, we are trying to say that these are groups that generally in literature are not as well represented as straight, white, able-bodied, cisgender characters. But yes, referring to such characters themselves as diverse, implies that they are other. So we can recognize that this is the term that people understand, while also realizing the term itself is problematic, and stating that a book contains diversity, is different than saying people - actual living people - are diverse for being non-white or non-straight or disabled or non-cisgender.