Fantastic.
- Your team is huge,
- the methodology looks quite wrong for it and chosen for its buzzword value,
- the most knowledgeable ones have been practically removed from the team (instead of disperded into balanced sub teams where they can contribute and lead) and sent on a magical quest on deep thinking island
Those three elements all lead to a single conclusion: your manager is acting at random.
...and you worry about the customer? I mean, the customer is the last of your concerns here, (and yes, it shouldn't be, on that we probably agree) but what I see here is: (pardon my french)
- a big fan,
- a pile of manure slowly falling onto it,
- and you in the middle, trying to toss your weight all the way into the fan.
Stay off the way of the old ones and their opinions, and take notes of how they and those opinions, affect your work, and the project, how, and when: heavy reorganization will come, and you'll want to have referentiable facts to support your position and role in the situation.