It isn't operator error, it is faulty ergonomics.
Suppose I designed a new jetliner that had two identical switches next to each other. One switch lowered the landing gear. The other switch shut off fuel flow to the engines. Such a jetliner would end up with a number of accidents where pilots mistakenly shut off fuel flow to the engines on final approach. That wouldn't be pilot error, that would be due to faulty ergonomics. You can design cockpit controls that enable accidents or ones that reduce accidents. The same is true for retention holsters.
FLETC and other ranges have banned Serpa holsters because they have seen more accidents with Serpas than with other holsters. That is due to the faulty design of the Serpa. The Safariland SLS design does not require you to push inwards with your trigger finger to release the holster -- as a result, it is a safer holster than the Serpa.
Last I heard, doctrine in most of the US military was to carry handguns with the chamber empty.
They don't. Some years back, I was doing a Tueller drill in a class in the meeting room at Harvard Sportsmen's. I tripped and did a full shoulder roll on the floor. I was carrying my 1911 in an open top kydex holster. The gun stayed put in the holster.
I can understand the desire for a retention holster if you are carrying openly. I don't understand it for carrying concealed.