For the most part that is very true. Chopper the animal doctor VS Doc Q and Stronger, the animal and the doctor. We don't have jobs for the newer crew mates but you can bet there won't be any archeologists on board. Actually I shouldn't say that because there very well could. Though my bet is Robin fights Pizaro the corrupt King. I guess all I can truly say is Brook and Lafitte just match up too well in style and presentation for them not to battle.
Judging from what we know, like epithets and abilities we can guess who will fight who but the job title plus fighting style only neatly lines up with about half the crew right now.
In the beginning I used to think that as well but if you step back a bit Jinbe is just one weakness after another. His greatest feet was having a 5 day battle with Ace and coming to a stand still. Of all the War Lords, Jinbe has been depicted with they least amount of over whelming abilities. Aside from Mihawk and Buggy[laughs], have you noticed Jinbe has no overwhelming 1HKO moves? He can't dry you out, he can't petrify you, he can't steal your heart(well he stole Robin's) and he can't rip shadows from you in an instant. Each of those characters has some sort of haxed attack that is very fitting for an antagonist but its clear Jinbe won't be doing any thing equivalent when he is front and center once more. Compared to Law, Kuma, Hancock, Mihawk, Moriah, etc, Jinbe has yet to display some outrageous feat of destruction. I'm sure he certainly can but I'm certain it's all intentional on Oda's part to make sure he fits nicely as a main character.
If we take it one step further, he was constantly seen failing until Fish Man island. He couldn't save Tiger, he never made it out to stop Arlong, he couldn't keep Luffy safe and on his watch he couldn't protect the mermaids on Fish Man island.
I feel like Jinbe's first bounty of 76,000,000 B(just 1 million below Sanji's), his team up with Sanji against Wadatsumi, and his relatively lack luster performance in the war(in comparison to the other War Lords who took almost no hits) are very subtle ways to show that Sanji and Zoro are more or less his "level" if not stronger than him now. He would fit right in the Monster Quartet.