I like the ‘should we be doing this’ as opposed to ‘can we do this’ attitude.
The limited field landing example appears to be a simple question of comparing RLD and RLA, then agree / disagree with the discussions above.
The exact content of the RLD may not be known. Does it depend on reverse, max brake, accurate threshold crossing height / speed / touchdown position? What airborne distance is assumed? Are all of these aspects achievable, all at the same time?
If the details are not known then at least 15% margin is required, possibly more.
There are other important aspects required for a decision – what is the wind, how wet is the runway (reporting accuracies); is the runway grooved, are there rubber deposits; is there an overrun area?
For a safety assessment before landing, all of these are aspects must be known. If there is variability, or areas of inaccuracy, then additional safety margins should be added, these could very quickly add up to the same factors as used for dispatch, thus this might be a good minimum if a more accurate pre-landing assessment cannot be made.
I suppose that the simple answer is if the aircraft was scheduled to operate to this airport, and if the legal dispatch requirements were met with full factored distances, then a landing at the planned landing weight would have a good safety factor – at or near full dispatch factors plus/minus wind, and the advantage of thrust reverse. So why in the example is the ALD / RLD ‘so tight”?