Your point 2. is actually very important and I haven't seen it discussed before. We don't know what instructions the drivers have been given, but there will be

Your point 2. is actually very important and I haven't seen it discussed before. We don't know what instructions the drivers have been given, but there will be first a question in the drivers mind about if the car will react. The driver has to consider if they will be reprimanded by Uber for breaking before the car had a chance to. So this might stop any kind of reflex action - which I assume is what the standard 0.5s reaction time is based on.