You mean the guy that has his own agenda and is confirmed to be an endgame player? Kuzan leaving the marine and becoming a pirate was great for his character after losinh his duel of ideology against Akainu.
There's absolutely nothing Ryokugyu would gain from becoming a Holy Knight . Contrary to the popular belief he does not worship the ground CDs walk on simply because he explained the scabbards how the outside world worked lol. He was annoyed with them for being in his way when RA captains attacked Marijoa.
What is actually canon is his pride in being an Admiral from the Marine HQ and his respect for Akainu. Why would Oda write him this way if he planned for him to change job? Meanwhile we knew Aokiji hated Akainu guts as early as the Robin flashback lol.
Issho, Kizaru and Akainu himself are more likely to leave than Aramaki.