I think your criticism of the term is somewhat valid, in the end these are just back-ends with APIs :)
However, the point the platforms are trying to make is that their APIs have been written with the explicit purpose of building a frontend ontop of them later on.
A lot of the old-school platforms have some APIs as well, but they are meant to e.g. import products or export orders. They are not meant to implement a frontend on top of, because they have a frontend engine as part of their monolith, and many functions you need to write a proper frontend will not be available through their APIs.
So the term "headless" means "we have APIs, and they are designed for you to build a frontend on top of".
However, the point the platforms are trying to make is that their APIs have been written with the explicit purpose of building a frontend ontop of them later on.
A lot of the old-school platforms have some APIs as well, but they are meant to e.g. import products or export orders. They are not meant to implement a frontend on top of, because they have a frontend engine as part of their monolith, and many functions you need to write a proper frontend will not be available through their APIs.
So the term "headless" means "we have APIs, and they are designed for you to build a frontend on top of".