Have you missed the entire chapter dedicated to explain how Kuzan joining BB is not a matter of strength, quite the opossite even. Kuzan joined after threatening Teach and beating half his crew in front of him.
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doesnt have to be
wouldnt voluntarily choose to follow someone who is less capable than he is and am not sure why this is even an argument. There is zero percent chance blackbeard isnt the strongest person in his crew.
Luffy will only fight one of those guys, Akainu. Fighting him won't be regresion.
the guy roughly equal to bb's commander ? unfortunately it is a downgrade.
as i said before, Blackbeard is 100% the strongest person in his crew aokiji included
and once luffy has moved past him he would be beyond them as well .
most of us also realize a role promotion doesnt necessarily put akainu on a stratosphere separate from those who shared the same job title he did 2 years ago.