Fighting beside anyone was never an indication of skill or strength. By that logic Luffy is Whitebeard 2.0 because they fought together at Marineford.
I will give you the reason why Sanji got paired with Jinbe, while everyone else got his own individual opponent. But I won't outright state it, instead I will give you a handful of panels illustrating my point. Maybe you come to the same conclusion.
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Robin joins the crew. Every member except Zoro accepts her.
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The following arc. Zoro and Robin are paired against Enel.
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Zoro cares for Robin after she got electrocuted.
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Robin cares for the defeated Zoro
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Forward to Enies Lobby. At this point, no one questions that Zoro honestly wants to save Robins life.
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Usopp gets beaten to the verge of death by the Franky family.
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Franky and Usopp get both captured by the CP9 and fight their way to Robin
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Usopp and Franky party hard.
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Sanj hates Jinbe because he thinks he is responsible for what happened to Nami
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Jinbe explains the situation, Sanji still doesn't care. I wonder what could make these 2 get along? Hm.
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Maybe a fight?
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Et voila, Sanji wants Jinbe to join (like everyone else on the crew.
You are right with one thing tho, Jinbe didn't overshadow Sanji (or anyone else).
Because that was part of the damn plan.
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Which was a) outright stated by Jinbe + b) confirmed by giving Luffy a bubble coral to battle a overdosed fishmen underwater. Don't you think the job would have been more suitable for…uhm...a fishmen like Jinbe?
As for the Shichibukai power discussion, there is a whole thread for that and I don't bother to repeat it all again. Tho it is funny that Moriah always comes up to show differences in SHichibukai strength, the only one who got singled out by Oda and was officially labeled weaker than the others. Apart from that, there is nothing that suggests a difference in power between the Shichibukai, apart from facefaults and stem expressions.
Edit:
So, it is a "pain in the ass" to discuss with me?
Alright, then don't do it. I actually went through some effort to explain myself, without insulting anyone. And if Corus feels insulted, sorry but that was not my intention.