Wordpress custom plugin ajax request not working

I wrote a jQuery ajax request. I've read the documentation regarding ajax requests and frankly it's not working for me.

I got it to a point that it is hitting the function and returning something.

This is the Ajax request:

jQuery('#ns-submit-comment').on('click',function(e) {
    e.preventDefault();
    jQuery('#comment-loader').show();

    var data = {
        'action': 'submit_comment',
        'new-comment': jQuery('#new-comment').val(),
        'ajax': true
    };

    jQuery.post(jQuery(this).parent('form').attr('action'), data, function(response) {
        data = JSON.parse(response);
        alert(data);
        jQuery('<p style="margin-bottom:0px;"><b>' + data.author + '</b> <small class="pull-right"><i>' + data.time + '</i></small><br>' + jQuery('#new-comment').val() + '</p>').insertAfter('#comment-header');
        jQuery('#new-comment').val('');
        jQuery('#comment-loader').hide();
    });
});

This is my action:

add_action( 'wp_ajax_submit_comment', 'save_comment' );

And this is my function that handles the Ajax request:

function save_comment($user_id, $article_id)
{
                if (empty($article_id) || !is_numeric($article_id)) {
                                wp_redirect(home_url());
                                exit;
                }

                $comment = $_POST['new-comment'];

                if (empty($comment)) {
        if(isset($_POST['ajax'])) {
            return json_encode(['success'=>false,'error'=>'Comment Empty']);
        } else {
            wp_redirect(get_site_url() . '/author-history/');
        }
                }

                $user = get_userdata($user_id);

                $time = current_time('mysql');

                $data = [
                    'comment_post_ID'      => $article_id,
                    'comment_author'       => $user->data->user_login,
                    'comment_author_email' => $user->data->user_email,
                    'comment_author_url'   => $user->data->user_url,
                    'comment_content'      => $comment,
                    'comment_type'         => 'editorial-comment',
                    'comment_parent'       => 0,
                    'user_id'              => $user->data->ID,
                    'comment_author_IP'    => $_SERVER['REMOTE_ADDR'],
                    'comment_agent'        => 'Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.0.10) Gecko/2009042316 Firefox/3.0.10 (.NET CLR 3.5.30729)',
                    'comment_date'         => $time,
                    'comment_approved'     => 'editorial-comment',
                ];

                $comment_result = wp_insert_comment($data);

//              update_post_meta($parent_article, "latest_revisions", [$post_id]);
    if(isset($_POST['ajax'])) {
        die(debug($data));
        return json_encode(['time'=>$time, 'author' => $user->data->user_login]);
    } else {
        wp_redirect(get_site_url() . '/author-history');
    }
}

Now all goes well until it hits the alert, where it returns the whole page. I use die(debug($data)) (debug is a custom debugger function) and that returns the whole page. How do I prevent it from returning the whole page and only make it return the data?