The aircraft performance is based on the equipment it has. If the performance says it can land safely in the conditions then the crew were unlucky.
A search of recent threads would show that the published performance for operations on contaminated runways cannot be relied on, particularly in relating the ‘actual’ runway friction to stopping distance.
Our industry does not maintain its excellent safety record with luck. Luck is where the safety factors are just good enough; we require safety margins providing defence in depth to accommodate the many threats to safe operations and the assumptions or mistakes that we often make.
If the performance says they shouldn't land then they f*cked up.
If a Captain elects to land in circumstances that appear to be outside of accepted limits then the activity is labelled as an error after the event. It would be more valuable to wait for an investigation to identify the error provoking situations or behavioural factors that enabled the Captain to make his judgment at that time.
Thrust reversers are nothing to do with it.
It would be foolish to dismiss the lack of reverse; see the recent posts in the thread on the 737 overrun at Midway.
JAR-25 NPA 14/2004 allows operators to take credit for reverse thrust on contaminated runways. Operators who do not have reverse due to MEL or equipment choice should make the necessary adjustments to the published landing performance, and in the latter case there would only be one standard.
“a useful braking technique”; the extensive discussion raised doubts about the value of the technique. In addition, it would not affect the published performance on which decisions are based and it is unlikely to make any significant difference in the actual stopping performance without additional landing risks.
The critical safety defences in contaminated operations are the decisions considering the landing taken before making an approach, not the dependence of non standard techniques or luck when on the runway.