I don't think Zoro ACoC is weaker or non comparable to Luffy's. However, Zoro is slower than his captain, his CoO is far worse and he can't use CoC for a long period of time apparently.
Advanced CoC is a very strong ability possessed by the very strongest but Zoro lacks many other things. He had to use that power against King not because King was actually that strong of an opponent but because he had no fruit to awaken or to master, he is not a CoO specialist, advanced CoA sucks, and there wasn't a stronger sword around. Not to mention Oda loves to wank his favorite swords(man)
I think Current Zoro is more or less comparable to Luffy. Beginning of Wano Luffy of course. ACoC won't fool me, it's a power up like manh other. It does speak of Zoro's potential tho