You guys are talking about REST but i think you don't even understand what it is and the fact that it can even return HTML and still being called a REST API.
Not saying livewire is REST, livewire's api calls to update the state and render components do no respect the REST architecture.
Just because it's JSON doesn't mean it's REST, the first REST api was created before json.
Before you even consider writing a "REST" api or give opinions about it you should read more about the subject.