@Lazy:
The pattern is whoever is an important/main character in the arc gets to go on the cover. The title was 10 vs 100,000, it makes perfect sense Jinbei was there. The volume cover is not a pattern unless it's true if and only if people who join get their own special cover and no one else.
I agree with rubia_ryu that the two year time skip makes Jinbei joining feel less natural. Nakamates always have that money where Luffy proves himself to them, or at least over the arc they join he wins them over (think, 'Sogeking, burn that flag down').
For Jinbei, that sort of happened two years ago, and it hasn't happened again this arc (yet).
Personally, I would like to see Jinbe as a strawhat. But I would prefer it story-wise if he stayed behind, because to me it makes more sense.
Have you and Rubia considered that between the separation and the War & the deaths that took place these entire last two years weren't supposed to feel natural either? I mean why should the recruitment process be any different? hell Oda threw us all for a loop when the crew was separated ,I for one thought that would never happen but it did and this is where the story took us.
We were bound to meet Jinbe on FI no matter what ,some even expected him to be the main villain of the FI arc [[myself included]] But clearly Oda had other plans ,he even managed to throw the story of Fisher Tiger in there before Luffy reached Impel Down,How convenient all right before Jinbe's introduction.
Tbh with you, without the Time skip I don't think he would of been a candidate considering how weak the crew was then compared to now,seems like Oda planned it this way.
Also I think someone mentioned this earlier,Jinbe has been impressed with Luffy both before and currently in this arc,He's totally dropped the Kun which is odd since that was kind of a trademark for their relationship.
Oda was never going to have the same recruitment process over and over. Before the manga advanced this far ,Luffy use to recruit people within a matter of five chapters or less but as the story went on the recruitment process kept changing and the time kept expanding ,instead of various chapters it turned into an arc or two then now if Jinbe does join it's like four arcs worth of development & recruitment ,but can you expect anything Less for an Ex Shichibukai or better yet someone who was already name dropped in chapter 69?