Which leaves the question of which is the dominant effect. But for that anecdotes are useless, because "I've seen this happen myself" doesn't tell you if it explains 5% of the difference or 95% and people have a tendency of jumping to conclusions without having all the information. If Alice made bigger sales to fewer customers and Bob made smaller sales to more customers and Alice is white and Bob is black, then if Alice gets the promotion the boss is a racist because Bob made more sales but if Bob gets the promotion the boss is a sexist because Alice made bigger sales. Or so you would think by only listening to the one complaining about not getting the promotion.

So then you'd want someone to do a study and we're back to anyone publishing a study that challenges the prevailing dogma getting punished for it.