The file chooser is a module version of the file browser, and the filebrowser represents the primary way that users interact with the file system, and as such should reflect the design of the file browser in terms of views, and sidebar padding and order.

For image focused tasks list view is so bad that I open files because dragging and dropping is faster than the filechooser, this wouldn't be the case with an icon view because in icon view having meaningful names for images doesn't matter at all.

The sidebar design in filechooser should be copied directly from files, I've spent a long time in files and my bookmarks are muscle memory at this point.