You are assuming that he acts by knowing that Yamato won't die like some character with 4º wall powers...lol
Kaido didnt try at all during this time. He could have used TB for each SN and gg. He could have used more power from the start against Base Luffy and destroy him, but they clashed for more than 20 minutes. He could have avoided to use his worst form for combat but he didnt. Etc.
So why the fuck will he try seriously to knock out Yamato when he didnt even did it with his real enemys lollll.
Still ACoC but he couldnt overpower Base Luffy and now we will see them clashing, with Luffy in G4, and Kaido will still be able to clash with him despite Luffy being a stronger mode.
So ACoC or not, it's irrelevant. First, because it depends on how serious will Kaido become, and second, since it's not a something mysterious for the reader anymore, there's no need to keep it hidden anymore, that's all, so he will use it at will.