The Brewster is slower than the a6m2 except below about 4k. I think that the a6m2 outturns it, but that's just based on my feeling flying the a6m2 and Hurricane vs. the Brewster. Anyway, the only other plane available would be the F4F or FM-2, both of which are faster than the Brewster. Also, the a6m2 is better than most of the IJ planes that were really there. Still, the IJ gets the a6m5 to help offset that the Brewster we have is a bit better than the Brewster that was there.
Given that the first two runnings of Rangoon worked out OK, and given that the Brewster is a better fit than what we used before, I think it will be OK.