You can display hearts on the photos by going to the view menu! (As well as titles if they exist, the file format, …) That info is overlaid!
(I also think it’s entirely reasonable to only have the thumbnail bar for photo navigation. I think the one in iPhoto worked exactly the same? It just maybe wasn’t displayed by default? If you give it all the functionality of all the other views there are consequences to that, knock on effects. For example, which image should be displayed enlarged if you select more than one in the bar? Keeping it simple keeps it simple.)
Ah, I see, if you turn things on in the view menu, it enables it to be overload ONLY in the main thumbnail view mode. When you're viewing a single photo, the heart/title/etc is not overlaid on the full size photo or the nav bar thumbnail.
(I also think it’s entirely reasonable to only have the thumbnail bar for photo navigation. I think the one in iPhoto worked exactly the same? It just maybe wasn’t displayed by default? If you give it all the functionality of all the other views there are consequences to that, knock on effects. For example, which image should be displayed enlarged if you select more than one in the bar? Keeping it simple keeps it simple.)