Hi Frank,
Good that the plugin can also be used for non-WP. But the reason that this plugin is so much less secure than the vanilla, is that it reads the database connection information automatically.
So where a bad guy would have to guess the password as well when using adminer, the adminer-wordpress-plugin does not have this protection.
If the adminer-wp-plugin uses wordpress-specific convenience features to allow access to the database, I think it should also use wordpress-specific protection.