Jinbe is...present.
I don't hate the character, but I'll admit he's probably my least favorite Strawhat.
I think the biggest problem with Jinbe is...Jinbe's just not very funny.
I mean, think about it. All the other Strawhats have some sort of running gag or character quirk that make their reactions to various situations fun. Luffy's a hardheaded moron. Nami's greedy. Zoro's a rageaholic who gets lost. Usopp's a coward. Chopper's naive. Sanji's a womanizer. Brook is dead. Franky's a weirdo. All solid gags that work in a variety of situations. Even Robin, who's probably the most calm and level-headed of the bunch has her shockingly dark or innocent imagination, depending on the moment.
Jinbe...doesn't have any of that. At least not yet, and it's getting pretty late in the story to add it in now. At most he's basically the straight man of the group. The serious one that others can play off. But, Robin kind of does that better, and can add in a touch of her own unique dark humor to really nail any jokes Oda wants to do. I mean, even Jinbe's gag with being the new "number 3" on the crew, is really more about Zoro and Sanji's rivalry and Sanji's reaction than anything Jinbe does or feels.
And battle-wise, yeah, he's in the upper half of strength for the crew. But, he really hasn't had a big, memorable fight scene like some of the others have had. He doesn't have a big, flashy move that I love to see him pull out against his opponents. At best, he's good backup to have. Like Jinbe backing up Zoro against Lucci on Egghead. He's good support. He's just not interesting fighting on his own.
It kind of feels like Oda wanted a Fishman on the crew for symbolic reasons. Probably mostly to do with the whole "racism" and slavery subplot of the story. But, kind of forgot to make this Fishman crew-member a interesting character in their own right. So, he kept putting off letting Jinbe join the crew, and now we're so close to the end. Jinbe just doesn't have a lot of chances to make a impact as a character, now that we're so heavy into the plot of the endgame.
Jinbe needs...something. Probably something lovably goofy that makes him memorable. I'm just not sure what. Maybe...collecting souvenirs from the places he visits on the surface, since he's never been to most of these places on the surface world before? Or maybe he keeps accidentally karate-chopping things he shouldn't? Or maybe he keeps "adopting" stray cats who keep following him around in these various towns? Or he squirts water on people when he gets nervous in social situations? Or maybe various people think he's the strong, silent type, when really he's just not sure what to say, so he keeps trying to come up with something in his own head? Or maybe he keeps building water fountains in random places? Or just being WAY too respectful and polite with his enemies? Something?!
Unfortunately, it just feels like it's too late to give him too much. Jinbe just feels like a bit of a missed opportunity, to be honest. He's on the crew...but it doesn't really feel like he adds much to the character dynamics, really.
But, to be fair, I think Vivi would have a lot of the same problems, if she was actually a part of the crew for a long period of time. Vivi's not "wacky" like the other Strawhats. I love Vivi, but I mostly love her for her goodbye on Alabasta, rather than as a character. The Strawhat's saying goodbye to Vivi is one of the all time great scenes in the story....but Vivi herself isn't really interesting, to me.
So, I don't know. I don't think we're going to get a LOT of stuff with Jinbe. Anything involving Jinbe will likely focus on him being a Fishman, rather than focusing on his own dreams or ambitions. Which is unfortunate, but it's honestly where the character seems to be headed.
Jinbe's more about WHAT he is, rather than WHO he is, and that's just a shame, really.