return content section as json in wp rest api v1

You can (and you should) always filter the output of WP_REST_API.

add_filter('json_prepare_post', 'change_this_into_a_proper_function_name', 999);
function change_this_into_a_proper_function_name($post){
    // hack and slash into your $post here. This is a regular WP_Post
    // add custom fields and tax terms you might need, remove what
    // you don't want to expose to app or are never going to need...
    // This filtering step is actually a must imho, as it really influences
    // the speed at which your posts will load over poor connections.
    // Special care should be taken with attachments, I usually replace them
    // with versions of 800px width (or even 600) for both Android and IoS.
    return $post;
}

The only app where I didn’t completely remove $post->content in favor of the excerpt was an app for a bookstore, where users were installing the app specifically to read book reviews. But even there, when pulling lists of reviews I was filtering the content out and only loaded it fully only on read more. It payed off. The app stayed agile even on poorly resourced devices.