In the dialogue with the Gorosei, Saturn says "ignore Sentomaru."
To which Kizaru says "I refuse, I have my own ideals to keep."
That's a direct contradiction to "I am just a cog in the machine."
Oda is clearly cooking something with Kizaru.
We got battleship bags and backstory with Kuzan and Garp, and we're clearly set up to get something with Kizaru.
Meanwhile, Kaido had one page of backstory.