As I don't have a penis, I really don't know, but castration sounds painful. For much of history it was done without painkillers apparently. Having any part of your body surgically removed sounds painful. I don't know. Castration didn't sound scary until I found out how it was done. In my mind it's as bad as female genital mutilation. I think the fact that he's an eunuch AT THIS POINT is more surprising than him being a guy.
Anyways, that's just me overthinking stuff. Thanks for the update!