So we go nack to the original question, Why does he NEED the training he got?
See the issue here. We know he hasn't even gone all out so this training must be extra special since we completely cannot gauge how strong he is from jump. It's like Oda is writing himself a blank check on how strong he will have Zoro be for whenever he needs it.
But then If Zoro is to fight King 1v1, there's no way it's as difficult as Luffy vs katakuri. And if Katakuri is comparable to King then Zoro having am easier time means he's stronger than Luffy was in the katakuri fight. Then that means there's a possibility EVEN BEFORE THE TRAINING, Luffy in WCI and Zoro were ALREADY COMPARABLE.
And the cycle continues.
The only way to break the cycle is to explain what Zoro training is needed for. That's the only way you can break out of this argument