It's not meaningful because the question here is not whether the algorithm reduces overall bias. The question is whether the algorithm introduces unwanted bias

It's not meaningful because the question here is not whether the algorithm reduces overall bias. The question is whether the algorithm introduces unwanted bias into the presentation of people's posts, with no ability for them to opt out. The bar would be different, in my mind, if we let people choose whether to use this algorithm or opt out. Also, as Twitter finally came to at the end of their post, the much bigger issue is that this algorithm doesn't respect people's desire to curate their own public image. Taking out the bias aspect, if I post a group photo that includes my best friend, and the algorithm crops them out of the thumbnail entirely, then that's going to be really frustrating to me. If I want to center a person of color or a woman (or an LGBTQ individual, which we don't know how the algorithm would rate - we don't have the data), and the algorithm makes a different choice, then my message is damaged.