PTSD is more than a layer of indirection, it’s a bed for the current direction of research focused on trauma. Shell shock isn’t a good term for home abuse for example, but the current dogma is that similar neurological mechanisms underly these different kinds of trauma, thus joining them all under the term PTSD.

The benefit of this umbrella term is, or course, contingent on there actually existing such a universal neurological pattern of PTSD, which I don’t think can yet be decisively established.