And what is Discovery if not an adaptation of the TOS universe, with modern visuals and sensibilities?
None of it is an adaptation. Not one of the stories, main characters or their relationships has been adapted in any way shape or form. And you cannot ‘adapt’ a text into the same medium, except in very specific circumstances (ie...adapting The Iliad into a children’s book version for example...or taking a film or tv show and remaking the exact same show in another country in a different language and location. That can sometimes lead to radical differences between two versions.) none of which is what’s happening in DSC. This is further apparent due to the fact it is set before TOS and there have already been other Trek shows, none of which were ‘adaptations’ either.
If you simply make a new version of an old film or TV show, it’s called a remake. Of course, once upon a time in Hollywood, scripts were considered more of a separate entity, so you could see those early remakes as something akin to an adaptation, but that concept hasn’t really existed for a very long time, and was nebulous at best..the industry was growing.
Words have proper meanings, even in specialised industries.
Yes, all the later series have ‘based on Star Trek’ in their credits, but it’s just a formality, as for a start, those are not based on ‘Star Trek created by Gene Rodenberry’ But are in fact ‘based on Star Trek: the next generation, created by Gene Rodenberry’.
DSC has much of its DNA from those shows also.
It’s a prequel, or if you prefer, spin off, set in the same fictional universe. Not even remotely an adaptation. It’s the same media. Nothing is being adapted. You can adapt a TV show into a movie, but that’s uncommon..though it still had some usage. You can adapt both into a stage play, radio drama, book...what have you. But those are different media, and had Trek started as one of those media, then been made into a Tv show, it would be an adaptation. But screen, specifically Tv, is the source text for Trek.