Easy: Kizaru explicilty said that the Snakeman was strong that he understood why Luffy had beaten Kaido.
Now, as agenda driven as one might be, saying this comment refers to some WC level Snakeman or even less than that (idk if you meant without FS too) Is between laughable and borderline sad.
On the other hand, there Is absolutely no visual indicator for AdvCoA or FS, so it's impossible to say from visuals he used or didn't use It.
To summurize: we have a dialogue hinting that he Snakeman was far stronger than just his WC counterpart and no proof that this Isn't true, aside agenda of course.