Agreed. The employee is rather judged by something like their peer's perception of how competent the employee is, their knowledge of the work the employee did, and their own belief of how important that work was, all filtered through their various cognitive biases about what work is important to the company and what a competent employee looks like.

There are so many of these biases. As just one example, studies have shown more talkative people are perceived as being more intelligent, even when this is objectively not true. I will take the time to find references if anyone's curious; I recall an experiment in which a group discussion was held and participants were rated by their peers on intelligence. The experimenters then measured how talkative each person was during the discussion, and their actual intelligence was assessed via a standardized test. Peer's perceptions of intelligence were uncorrelated with actual intelligence, but strongly correlated with talkativeness.

The result is that fast talking employees who focus on impression management, self-promotion, and securing juicier work - work that is of a quality or type more likely to be perceived as being important - at the expense of getting genuinely important but often less glamorous things done, and less things done overall, get rewarded.

This problem is particularly pronounced in American culture where extraversion is already a highly regarded and arguably overvalued trait (e.g. show and tell). It's less of a problem in other cultures, e.g. European cultures, that place higher value on introversion (e.g. quiet work and study).