I’m guessing it’s a pretty huge factor. Chance of passing is going to be weighted for amount studied and luck. What else? Strategy has a lucky component, level of retention is dependent on what they ask on the test and if you were lucky enough to remember it.
If you study enough, luck will become decreasingly important, but that is far and beyond what most candidates have time/energy/focus for.
It’s natural for ppl to have strong and weak areas. The luck comes in by whether or not “your” material is on it. Someone could get a 55%, do zero additional studying, and then get a 75% just by having the material go their way the 2nd time. Obviously the idea is to know everything, but just saying.