Headless or not, there is just no way to create a one-size-fits-all UI framework. With any framework you always end up one component short, always have to reinvent the wheel at some point and always have to compromise.
The idea of Vue Composable UI is to abstract functionality, not components. This way you do not have to adopt any kind of opinionated UI paradigm and do not have to recreate basic UI functionaly for application-specific components that are not present in frameworks.