There should be a way to handle ajax requests without the downsides of admin-ajax.php
I guess this file has not been intended to how it is used.
There should be a way to do effective ajax requests without loading all plugins, without require the wp-admin folder to stay in place (can also not just be protected by basic auth because of that dependency) etc.
Having a standadized way to handle ajax calls is a good thing and should be possible.