This article is actually a very strong argument for diversity in boards.
Co-advisors should be on an equal footing in terms of the power dynamics. They can discuss amongst themselves any advice that they feel might be obstructed by biases and should be able to do so frankly. If others in the advisor group agree on the advice, then they can then present their advice as a group rather than as an individual to the person they are advising.
At that point it doesn't matter who the person is breaking the news. The advice comes from a group of diverse people and is then far more defensible against accusations of sexism, racism, etc..