Yes, the WP Rest API is much more complete and updated. Not found in the other, for example, a good solution for custom posts. Already in the Rest API this can be done easily, and many other filters.Then take a look at the documentation! Very worth it!
You can find the Jason Data within the index file of your website page, It is a small scrip you can check, before adding Json, I will suggest you to work on Staging environment for WordPress because during the installation process, Json Data might be lost.
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