! EDIT: holy shit this post is long as balls. You guys don't have to read this, these are just my personal opinions on this arc as a whole as well as Jinbe's joining. Sorry if i get in any sort of trouble due to the length or anything cause of this post.
! Ok. I am not really a new member, I have been on Arlong Park Forums lurking for like 2 years now. I really only go to the spoiler section, of course, but because of all this Jinbe stuff I got motivated to post here. As these are my opinions, I understand they don't really hold any water for anyone, but feel free to go ahead and read them.
! Firstly, I want to say that, I like Jinbe. I think he's a really cool character. But at the same time, I can understand where the jinbe haters are coming from. He's not exactly the most interesting man in the world (when i drink, i prefer dos equis), and I agree that for him to be a strawhat is an odd choice. However, having said that, you guys have to remember that oda is an author, and because he is a story teller, every arc must have some meaning and purpose beyond the obvious.
! I also agree with many people here that fishman island was passable, not great, etc. However, since I have worked on a shounen manga of my own a while back, I take a step back and try to analyze it from a broader perspective. I think a lot of why people don't like fishman island is because of hype. Point being, that Oda set up Fishman Island for so long, ever since Water 7, that when we finally got here things did not meet everyone's expectations, even subconsciously. This could either be an intrinsic problem of the arc itself, or the hype surrounding it. But from a story standpoint, Fishman Island accomplishes a lot of things.
! It more clearly defines human-fishman relations–wrapping up that plot thread since Saboady--and showcases the Strawhat's massive powerup since the time skip. Maybe pre time-skip, Hordy Jones might have been an admirable and powerful villain, who would have given the protagonists a lot more trouble, but after the time skip, he's nothing. If the strawhats cant even handle a villain like jones and his crew as easily as they did, they aren't ready for the new world. But all of these facts are easily discernible to everyone. I look at this like a dialogue heavy episode of the Walking Dead. I know, weird analogy, but in that show not every episode is filled with action. Some are just filled with dialogue, but they have to be in order to set up events for future episodes.
! That's how I view fishman island. On its own, it's not great, but in the grand scheme of things, who knows? It could very well set up things that have major ripples later on, and if not, at least it served as a link between pre time-skip strawhats and post time-skip strawhats, in terms of their powerup. And it also finally concluded a lot of the plot threads about fishmen that were set up even as far back as Arlong. But I agree, that, on its own it was not as good as previous arcs, and considering the absolute amount of hype surrounding Fishman Island since Water 7, maybe it could have had a bit more flair and fireworks. Although I think that the final scene with the blood transfusion was very moving. Ah, well, perhaps in this case it is about the journey and not the destination? This arc wouldn't have been nearly as fun if they just headed there right after saboady instead of getting separated like that.
! You guys, you have to take a step back and remember that One Piece is a large scale manga. There are going to be more arcs, that are probably better than this one, but in order to get to those we have to endure arcs like this, that serve their purpose of solving plot threads and showing off what the strawhats can really do now. And, as far as Jinbe goes, I am also okay with this decision.
! If you, the reader, understands that for a person to join the straw hats is a big deal, then how much would the AUTHOR understand that same thing? Do you think that Oda just impulsively decided Jinbe would join the crew? He may have decided this ever since Jinbe saved Luffy's life in marineford. And if that is the case, then Oda has most certainly come up with some way to make Jinbe work. Think back to when Robin joined. Did any one here think, "Oh man, Robin, she's totally straw hat material and she's definitely going to go through a lot of development later on!"
! I didn't think that in the slightest! When she joined, I was like, "the fuck?" It was weird! and out of place! And she had absolutely no character development before. The only thing good about Robin joining back then was that she was easy on the eyes, and had a cool power. Give it time. Who are YOU, as the reader, to dictate who is straw hat material and who is not? Are you the author? Are you psychic and can read the future? You don't know if Jinbe might do something cool later on that solidifies his position in the crew.
! Anyhow, long story short, there is no other major straw hat ally who has gotten as much screen time as Jinbe. He was mentioned as far back as Arlong, and has been a major player in 2 and a half arcs. Let's not forget--even though it wasn't their fault--that when Luffy went through the most horrible event of his life, it was Jinbe who was there to remind him that he still had his crew. It was Jinbe who was there to comfort him, after saving his life like three times. What Jinbe adds to the crew is not silliness, but not every character needs to be goofy. Also, his shock reaction to Shirahoshi was brilliant. He has his own spice to add to this crew, his own distinct personality, which may be calm and in some ways boring, but I still look forward to his interaction with the other members of the crew.
! He did more for Luffy than arguably any other major straw hat ally. And out of all of the major allies, he's had the most development so far. Personally, I can't wait to see what he will do next. Oh yeah, he's also freakishly powerful, which they'll need for the new world, and we've always needed a fishman crew member.
! But last thing, I do agree that I would like to see a more tragic backstory and dream, but there's still time to set that up, I think. I mean, Brook's dream wasnt even revealed until the tail end of Thriller Bark, and neither was his backstory (recall that the Rumbar pirates dying backstory was revealed after they beat Moria). As far as crew position? Go read One Piece wiki article on Jinbe. They call him a very capable "Helmsman".
! And before you give me shit for saying Jinbe can be the Straw Hat's official Helmsman, go take a look at one Jesus Burgess. His infobox back in Loguetown called him the Blackbeard Pirate's Helmsman, so yes, it is an actual and badass position to have.
! Give Oda some credit and time, it's not like this is the last chapter of one piece. I hope that Oda uses the next couple of chapters to flesh out Jinbe more, give him a stronger backstory and some dream, and let's get this show on the road, cause it's finally time for New World.