Change default from “Attachment post URL” to “File URL” in Add Media

Youre almost there. The func I show in this thread sets the ‘large’ as default, but also, in that thread, you’ll see

There is a hidden options page in WordPress under yoursite.com/wp-admin/options.php On that endless list of undocumented options you can set a value for “image_default_link_type”. You may want to set it to “file” (without the quotes)