Acutally, in case anyone lands on this page, I found a universal useful bit here.
function my_prefix_comments_open( $open, $post_id ) {
$post_type = get_post_type( $post_id );
// allow comments for built-in "post" post type
if ( $post_type == 'post' ) {
return true;
}
// disable comments for any other post types
return false;
}
add_filter( 'comments_open', 'my_prefix_comments_open', 10 , 2 );
The conditional check can even be outside of the handle and we just use add_filter( 'comments_open', function(){return false;} );
Graceful.