Honestly, Law's Haki mastery is quite good at this point. He learned how Kaido and Big Mom use their Haki as a passive barrier to block or defend attacks, even some hax ones, and Law used the same ability to cancel hax.
If Law gets ACoC, I'm pretty sure his ACoC wouldn't be weaker than Big Mom or Kaido. I mean, Law has better Haki feats than Kidd and the latter is a conqueror lol.