Backface soft armor also catches spall, which can be very dangerous itself. Even ceramic plates can have a danger of ceramic shards. I believe modern ESAPIs, XSAPIs, and such modern plates are designed stand alone, but original SAPIs carried a warning that their rating was only in conjunction with soft armor.
To add to your point, trauma pads exist to help mitigate this. Blunt force trauma is no joke.
Backface soft armor also catches spall, which can be very dangerous itself. Even ceramic plates can have a danger of ceramic shards. I believe modern ESAPIs, XSAPIs, and such modern plates are designed stand alone, but original SAPIs carried a warning that their rating was only in conjunction with soft armor.