No, it’s not okay to lock down or block access to wp-admin and/or it’s sub-directories. Not only you already mentioned this is a crude method, it could and most likely will break the site, depending on its theme/plugins.
The reason is that some plugin or themes depend on either admin-ajax.php or admin-post.php to accomplish some tasks. That’s why there are additional global variables in your source.
For example, the pvcArgsFrontend variable belongs to the Post View Counter plugin, which uses admin-ajax.php to update a post’s view count. If you block wp-admin, you know what happens.