Maui, first, the changes in calculating landing performance were driven by the need to address one, of not the most serious safety risk in operations.
I did seen a comparison of the new performance base - OLD, against the certificated (AFM) performance - more searching to do (Boeing / Airbus, TALPA meeting?). The performance data were remarkably close which suggest that the industry, those operators not using the full landing factors, have been exposed to significant risk, which in some circumstances have been borne out by accident figures.
Second, the simulator is a model - it is a representation of an aircraft and not reality. A manufacturer may only have dry landing performance for comparison because this is the only requirement for certification, yet that data probably does not account for differing runway surfaces or brake wear ... and particularly piloting operation and perception.
There is similar variability with aircraft and actual operation, but there should not be such a great difference on a dry runway. However on wet runways and particularly contaminated runways there probably is much wider variation.
Always consider how representative a landing may be vs the method of calculating landing performance - speed, wind, TCH, float, spoilers / reverse timing, brake/tyre wear, runway surface, ...
Nothing is ‘accurate’ in aviation, just an approximation which pilots have to manage. Having a bit more margin to help manage the unexpected reflects an attitude to safety, which if maintained negates the need for liability.
# 6 [ Exactly what are 90% of Airbus pilots not aware off? ]