In my opinion, if the people who work with someone consider them incompetent, they likely are. I would even go so far to say that the opinion of coworkers might

In my opinion, if the people who work with someone consider them incompetent, they likely are. I would even go so far to say that the opinion of coworkers might be the best predictor of someone's competence, better than any "objective" measure. At least if the people you're asking are themselves competent in the skill they are judging (asking the dev team whether someone is good at sales might not be predictive).