You say "Faces rule. Faces connect". I understand that. Are there not some (mind you probably not many) cases where not showing the face adds to the interest, mystery. And I am in no way trying to suggest that this is the case in my picture.
Imo, all elements in the photo should contribute. This is the best case scenario. Good painters don't paint extra lines. They also rarely paint people from behind. The great Karsh, I believe made only 1 portrait of the back of someone. (And still made sure to get other angles)

Street photography is different is some ways, but identical in other ways.
If you are including a person whose face we can see - that usually helps the comp if, exposure and other features of a good photograph are there. If we can't see a face but we see a strong gesture...that works. If we see no face but a strong silhouette...that can work too. If we see no face and no gesture we need 'more'.

If there is no gesture, and no face. and they are in the center or on the thirds.... Then imo, you are normally guiding the viewer to a boring place.....my solution is often to wait for the gesture....or move on, or shoot the scene without them in it.

Backs of people are like extras in a movie....rarely will the movie or image be stronger if they are included in an area normally reserved for a (more exciting) focal point. If they are in the background, and they don't detract...that's cool because they aren't stealing our attention with their backs.

Just my opinion here...