How do I get more image editing options in the admin?

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This is correct. To have the Restore Original Image, you need to alter the image first.

Also for the thumbnails, if if ( $thumb && $sub_sizes ) condition is not met (if the image doesn’t have thumbs) you will not see the thumbnails section.

File: wp-admin/includes/image-edit.php
143:    <?php if ( $thumb && $sub_sizes ) {
144:        $thumb_img = wp_constrain_dimensions( $thumb['width'], $thumb['height'], 160, 120 );
145:    ?>

BTW, WordPress 4.5 Coleman, has been released 2016-04-12.
You simple track the changes and nothing serious happened from then till now.

For instance, I created a really small image 5x10px, and when I enter the edit section I don’t get the thumbnail section. Image too small.

No thumbnails section

You may add 

add_image_size( string $name, int $width, int $height, bool|array $crop = false )

inside your theme. Low values for width and height may inject the thumbnail section.

This post is not super relevant but it may help.