@kmohyudin:
Good post!
But for one thing don't you think tier exist in Sichibukai for example Mihawk has been known to be a rival of Shanks, it has not been shown or anything but it can be deduced that his strength is closer to Yonkou level.
That puts the question of how the Sichibukai are ranked amongst themselves.
For instance again a Mikawk level Sichibukai wont be joining the crew…
Hancock has been shown to be strong, how strong, we have no idea.
All 7 are not created equal. Blackbeard reeks Yonkou level of power. Mihawk is also strong as a fighter.
Blackbeard aside, being Shichibukai is a mix of influence, notoriety, and personal strength. Mihawk doesn't appear to have influence, fitting his character. Flamingo, Jinbei, and Crocodile seems to be the bar for an average Shichibukai. They are on par with the Supernova in strength, but with more influence and notoriety.
Hancock lacks the strength and notoriety. Her personal strength would be her fodder stomping abilities. However, in duels, she is not necessarily a cut above Strawhats when they unite again. Hancock's personality isn't currently represented at all in the Strawhat crew. We have neither pompous queen type in the crew nor the lovesick puppy.
Jinbei would be a little on the strong side for the Strawhats. Him as a temporary member akin to Vivi seems more likely, as he is a responsible person and has a responsibility unlike Hancock. Jinbei brings to the crew power in water. He is a Fishman, making him the next unique member of a motley crew seem likely. His personality type does over lap Zoro's a bit.
Crocodile is too evil and world weary to be a fit for the Strawhats. He also has his own ambition in controlling and ruling more so than freedom. His sand power is also too powerful for the growth of Strawhats. He is a definite no.
Other potential members we've seen so far are either too one dimensional to compensate for their weakness. We already have Usopp who is 100% no frill guile and wits. Having another weak character who only stays alive through being versatile and being lucky would overlap with Usopp's role too much.