I doubt Zoro has full control of it when you analyze Gaban's words.
He says the true power of haki comes out when you are able to identify it and control it.
If Zoro has full control over his CoC,why is it always leaking from him? He doesn't have his CoA oozing aimlessly for example.
The intent from that convo seems clear: Zoro is finally conscious he has Coc,je stops leaking it aimlessly by controlling it and his true haki power comes out as per Gaban.
Luffy is already conscious of his and thus his haki is already at its current max output.