Headcanon. He still is a Marine Admiral. Luffy and Garp clashed and they are family. Luffy and Koby clashed and they are friends. Luffy planned on fighting Ace too. Theres nothing justifying Fuji being an ally, he still hates pirates, supported the Serephim creation, and like every other marine, doesnt know what dangers finding One Piece poses for the world. You have no idea how he'll feel when Luffy is close to being PK. His "good" status may come after losing, not before.
And just like how Zoro didnt defeat a Yonko Commander before Luffy, Zoro isnt defeating an Admiral before Luffy. Its tiring having to explain this basic logic to people. This was basic logic explained to you with Kaido and King and you refuted it. He's not even relevant to Kizaru at all right now lol