The back kick (done correctly) has a huge advantage built in. Because the kick is delivered before the rotation comes around it's a very deceiving strike, and often is out and landed before the opponent reacts.

Even in MA combat sports, many people actually throw a spinning side kick, and call it a spinning back kick. On the street, it would be very effective against many opponents.

Now, I wouldn't call it a first line technique, but I would by no means take if off the table.
Undefeated in all of Asia!