Jeanne in Apocrypha is a strange case anyway.
Many of the other pseudo-servants we see are Divine Spirits that are too powerful normally to fit into a Servant container (Euryale and Stheno are an exception as really weak Divine Spirits), so they instead use someone else as a vessel, someone with a compatible nature and a connection to a holy grail (war). And the host is usually pushed aside by the stronger Divine Spirit but often its a merger rather than complete loss of control.
No idea why Zhuge Liang is a pseudo-servant, I thought he was just human. But then most pseudo-servants are mainly just excuses to bring in popular characters from previous Fate works anyway.