Here is the fun part for you my friend and why your argument is BASELESS
The whole thingy of "Kaido was apprentice" was not mentioned by Sengoku. It's "Fake Spoiler"
The same way the "fake spoiler" of Moria reduced a lot of Kaido's forces before Oden faced him.
The only thing that Sengoku mentioned about Kaido was the same as Big Mom, which is... they were at their "younger days"
here is the page for you. So do not use the "apprentice" excuse with me, please. Unless you bring me Viz translation which I don't have my hands on it now and it says otherwise
You guys are using "apprentice" excuse when it's not even a proven fact