Shanks is not one of the Roger Pirates that made it to Raftel though. From the perspective of the final step to reaching that place, and how a Roger Pirate feels about what they have found out there and what that would mean for BB or Luffy, Shanks would be less fitting.
We have absolutely no reason to care what Scopper Gaban thinks about Luffy getting to Laugh Tale though. It adds nothing to Luffy’s journey, when we’ve already seen both Roger’s right hand man
and the one he gifted his hat to put their faith in Luffy.
We have every reason to care about what Shanks thinks about it, given that’s been the purpose of the series since literally the first chapter.
Even meeting Crocus again after Laugh Tale will have much more meaning than meeting Gaban, since Crocus and Brook have a history together and it accomplishes Brook’s dream.
There’s just no point in adding in another Roger Pirate at the very end of the series, one who’s been irrelevant for the 90% of the story previous, when Shanks, Rayleigh, Crocus, and even Buggy, have already have well-established relationships with Luffy. Those guys (minus Buggy) have believed in Luffy since he was a child, a newbie to Paradise, and a big name rookie.
Rayleigh would be fitting, but he would not be there to provide that interaction in real time.
Well, Rayleih could get a boat after hearing Luffy beat Kaido and head out to meet Luffy. Would make as much sense as Gaban randomly showing up and mean far more to Luffy.
Scopper could make that decision by himself, not follow Roger's order.
Maybe Rayleigh is casual about it because he believes in the profecy, while Scopper wants to see with his own eyes this special person and crew that could achieve what his captain and they could not.
Or he can read it in a newspaper like everyone else.
We’ve been waiting all this time for a Luffy/Shanks reunion, not for a redundant Roger Pirate to show up and say what people in-series knew years ago- that Luffy is the one Roger is waiting for.
Either Gaban has some unique purpose or he doesn’t show up. Being at the end of the Grand Line is not unique when we’ve known that’s where Shanks would be since before we knew what the Grand Line was.
Wouldn't BB be able to go straight to Raftel if Scopper had joined him ? Are you envisioning a scenario where Scopper demands of Blackbeard to still take all the steps necessary to get the information without his help, to prove himself worthy or something ?
Something like that. Gaban watching Marineford, coming to the conclusion that he’s who Roger was waiting for and joining up with him. Ray didn’t tell Luffy how to get to Laugh Tale, it‘s pretty easy to imagine Gaban doing the same to Blackbeard and telling him to leave it to fate, since that’s the Blackbeard Pirate’s thing.