Is the chief of staff an ancient strategist?

You can say that, but there is a difference.

"Military adviser" is an early operational consultant, but it is not a full-time officer, but a title for "intelligent talents" who participated in combat in a specific period. The functions and powers of the "military adviser" are also relatively casual and broad, mainly assisting the monarch.

With the modernization of war, fighting relies more and more on "intelligence" rather than "strength". There are gradually "staff officers" in the army who study war full-time, and "chief of staff" is a concept after the era of hot weapons. It directly participates in the operational command of the army and helps the military director of the army.