He's always been my least favorite, Robin's flashback made him seem very whiny to me. Compared to a moral admiral like Fujitora, Kuzan's barely even trying to do what's right too.
Well yea he's more pro Marine than Fuji, being a marine lifer and all. So it'd be harder for him to outright act out against them like Fuji blatantly does. So it's cool.
Tbf to him too, I think the shot at FA was the first time since Ohara when he was fired up again, deep down inside he still probably had Fired Up justice but in order to cope with the situation he just fell back on Lazy Justice. When he fell to Sakazuki, the only glimmer of hope remaining to change the Navy from within was gone, and he would have to fall back on Lazy Justice but with no end in sight this time. So he defected.