Say, well sorry for bringing this again, but didn't have time to reply before. This is not a rant, btw, but my apologies if it comes out as one:
I think the problem that makes Jin's development seem halted is not only he still has the niisan mde untouched, he is overall the same outside wanting to chase down Tsubaki. While it is understandable if you think that they aren't rushing things so his growth comes as well done, I think it wouldn't have hurt to have some hints he is getting better; for example tone down the nisaan mode a little bit, or reduce a bit the jerkyness. Then again in CS he went on a whole new level of epic in just a few scenes, so I guess some misunderstood (myself included) some moments of inspiration as some geniune instant growth. But also, he did leave to train with Jubei for a while, so it makes sense to think the old cat actually helped him to overcome a few things in their time together, use his powers or something, everything pointed out he was working on his issues directly aside his epic moments in CS, so the slow process comes as confusing given all.
However, this "pacing" argument you can use to justify's Jin's "slowed" development doesn't seem to apply to Noel who is shown to be quickly overcoming her fears and becoming brave. That's not a bad thing, she really needed it and I really like she's actually becoming competent.
Say, this is more of a personal thing, but personally what makes me worry a bit too much about his growth is his overall "small" role in the story so far, despite being promoted as the game's third main character after Ragna and Noel. In CT he was posed as a threat to be swatted aside by Ragna, in CS it wasn't until the very end he went into the main heroes wagon, but so far there have been only setups and people saying "you will be important"m but nothing really has paid off. Now comes CP and while he is in the quest to save Tsubaki, everything points Noel will basically be the one to get it done, no mentions to the power of order, no mentions to his involvement in the Ikaruga war, even his romance with Tsubaki has been barely explored by his side of the story, we get many thoughts on it from Tsubaki though. If Jin wasn't promoted as a main character there would be no problem, though. Interviews that mention how Ragna and Noel and Saya will actually have relevance and keep leaving Jin out despite he is also part of that family can make you really paranoid with this whole deal (then again I am aware that's a personal issue).
You can argue that Hakumen covers Jin's lack of importance, but I dunno, I really can't unsee those two as completely different characters, not only they have different personalities, they exist in the same time and space, they have different lifes that shaped them differently.
I am sorry for the long post and for insisting on this point. Carry on, guys.