Friendly reminder @MarineHQ thinks Kuzan is stronger than Borsalino
Oda literally called Kuzan ed Akainu "Monster recruit" and long term rivals.
You must understand the Dynamic of Kuzan vs Garp, Kuzan was suppressed, he could not make both Garp and Coby go away so he respected his mentor's ideaology (and yes, he's aware of It and seen in the flashback), so Kuzan literally made Coby go away when he could have used Ice age as confirmed by Pizarro.
Kuzan worried the whole time about Garp.