4 .50 cals isn't exactly a meager armament... the P51B, Wildcats, and P38's (I know the P38 has a Hispano but from what I understand people continue to use the 4x .50's once that's dry) are fairly popular aircraft, I don't see why the Brewster won't see at least some use, with a similar crowd to the Wildcat. (the .50s are M2's, right, they weren't replaced in Finland?)
4x .50s is at very least a superior armament to that of the A6M2's, not far behind the A6M5b's IMO... especially in a turn fight.