I think your point about humanocentrism is extremely salient. I didn't really think about the fact that the Cerritos has the most non-human crew members until you pointed it out. Obviously there is a meta reason for this (it's easier to draw aliens than to put makeup on an actor) but if we take it at face value then it has some interesting implications. Humans are more likely to rise through the ranks to serve on more important ships like the Enterprise while non-human starfleet members are often relegated to less prestigious ships like the Cerritos. Furthermore, aliens which appear more human are also more likely to get the best postings (think vulcans, bajorans, etc).