Aye, I have been seeing an argument in this thread about how "Kaido is a might makes right character so he doesn't need to be a complex character".
About that...
First off, there is no solid rule of writing that decrees that a "might makes right" character cannot be a complex individual.
Secondly and far more importantly, I have not seen one person criticise Kaido for not being complex. Kaido isn't criticised due to a lack of character complexity, the main criticism is that he is bland, boring and underwhelming.
How many popular One Piece antagonists are actually praised for being complex characters? The only one I can think of is Doflamingo.
Alabasta Saga's main antagonist in Crocodile wasn't complex. The man was just classic, power hungry, manipulative villain energy played straight.
Skypiea Saga's main antagonist in Enel wasn't complex. The bloke was an egotistical, narcissistic, megalomaniac high on a self-deluded God trip.
Water 7 Saga's main antagonist in Rob Lucci wasn't complex. The guy was a sadistic, bloodthirsty, straight laced assassin that followed orders to the letter.
None of these guys were complex characters when they were Saga/Arc antagonists and none of them had any sympathetic character traits. They were all unashamedly villainous to the core.
All of these characters are far more popular than Kaido and it sure as hell isn't due to their "complexity" because they haven't got any.