I get what you're saying! And I think that that might be some of the confusion here:

But when B's player is trying to find opportunities to involve B in the plot, and they're investing heavily into ranks because they believe it will push B into central plot focus whether B wants it or not, it will be very frustrating for them to be passed over for A and left with nothing, especially if the reasons why are never articulated or clarified.

I feel like ranks give you more ability to have your character do stuff and be in charge and have responsibility but doesn't automatically come with the guarantee of plot hooks or information. I've always taken it to mean that your character has earned more trust within their faction, so in Ryouma's case getting the faction to back him on a deal when he's earned 3* is way more likely than it would have been if he'd tried to do it with 1* as the narrative is concerned.

There is probably no way to guarantee that just because a character has a certain rank that they're definitely going to get plot relevant information because that's hasn't been the purpose of them so far? That's why OOC activity = IC rank always made sense to me because the idea that your character is being active enough to "buy" more influence in their faction is exactly that: people see them out there and are more willing to work with them and not just because they're lieutenant so-and-so. Sort of the "I know a guy who knows a guy" type deal. If you have 3* a lot more people are gonna know you're the guy and you're trusted. I absolutely get where you're coming from how this can be confusing on an OOC level especially if you're new though, so it's a hard balance to strike.

I guess I'm hoping that this might help as a suggestion, if nothing else!