Doman was perfect.
John Doman was the perfect man for the part. At first it came across as grating, yes, as did many things in the show. At first I couldn't stand almost any of the characters, actually, but I could tell it would be great if I kept watching, so I did. Character develop makes this show, any annoying nuances from the characters are eventually used to solidify who they are supposed to be. John Doman captures the evil, insanity, sorrow, and even kindness of Rodrigo Borgia perfectly, I actually couldn't imagine anyone else pulling it off in such a meaningful way.
Especially after Rodrigo dies, anyone else as Pope just does not capture the same essence that Doman brought to the role.
I can't imagine The Borgia's could be remotely as good as this show ended up.