I think Gaban is basically the baseline top tier haki guy: Stat wise very versatiled, good fighting style, advCoC and basic FS.
The more we go on the deeper the ability pool will become: sword shenanigans, higher CoC powerlevels, abnormal lvls of base strength and DF abilities as a synergetic component, advanced haki blast applications, WiFi haki, greater FS, different fighting styles..
It's like a catalog Oda can pick from in order to put together his different top tiers.
I've said it before but base Kaido was already a high ceiling for a guy like Gaban as he's physically (much) stronger and faster, while he already had the basic top tier haki set down aswell.
His blunt force AP was just shit, that's where Gaban has him. But Kaido with an Axe would have ended the story anyway, so..