Yes it is because I have a deaf daughter that I am somewhat sensitive on this issue. Despite her compensatory more highly developed visual skills than you or I she knows and I have to agree she is at a disadvantage of being aware of danger.
People who think 'looking over your shoulder' is a complete solution are deluding themselves. Building a picture of what is around you is always incomplete. You try hard but if there is something dodgy ahead you may need to forgo the glance back. And any lifesaver should be to confirm what you already think is there. Goodness me the state of the road, watching for and dodging potholes can almost be a full time activity.
That's why, unless you don't have one, it is unwise to rely on one sense alone. There may be no time for that lifesaver. Which may leave you, and the person behind ...