> What kind of criticism is "no need to have Dracula in space"?

It's more of a literary criticism, I think.

I get the vampire is meant to be part of the diversity of human nature in the crew.

The problem for a lot of readers is it's distracting while not adding anything substantial.

It's more like Watts got some glee out of updating vampire mythology in the future, rather than deeply serving the plot. The vampire could have easily been replaced with a genetically-engineered super-smart psychopath, and nothing important would have changed.