The REST api will make sense for everyone when Themes and app leveraging it will be showcased. There is still only few tutorials on how to use it for now. When you look at the CPT or the customizer, there are still developer tools. Although with plugins like ACF or Pods, more and more people will be able to use it. These API are definitely great for developers but what matters to end users it's what it does for them and how they can use it.