I think it's unacceptable for automation to produce a worse result than a human in the same situation, with the same information. i.e. it's not acceptable for automation to fail danger, it must fail safe, including even if all it can do is give up (disconnects, warning tone, hands control over to the human driver). I think it's reasonable, in the narrow case where primary control is asserted and competency is claimed…
First, a human who is paying attention makes better decision than a human who is surprised by being given control during a crisis. Therefore if automation sees a crisis, it's standard has to be that it is worse than a surprised human, and not how it compares to an alert driver.
Second, the analysis that concludes that we're now in a specific situation where a human would do better is often beyond the powers of automation. For example it can recognize that we are now in a class of cases where, on average, automation does better. But whether it will in any particular case may be beyond its reasoning power.