How to clone all WordPress Rest API end points

There is nothing wrong if API returns more than what you need. Unless there is a security/privacy issue it is unlikely that the additional info will matter.

If you totally can not live with core’s API, you need to just write your own. “cloning”, “forking” or any other nice term you might want to use will end with you having to take full responsibility on the resulting code, therefor you might as well approach it from an “I am writing my own code” point of view.