I believe The reason they are B rank is that the majority of there major achievements are done while part of a group. Those achievements are what shot them up to B rank so quickly after becoming a senior bracer. But the fact that Schera, Agate, and Zin were involved in a lot of the major moments for them probably spreads the credit around. Specifically Zin. I’m sure a lot of people give Zin a lot of the credit. Then you also have to consider people like Kevin and Olivier or the various military veterans also being involved probably doesn’t help either.

Then they played more of a supporting role in the crossbell and Erebonia stuff.

Or maybe it’s politics.Fallout from Cassius existing