Sure, they might be "good enough" but thats not the same as saying they are "as good or better". No firepower equation is going to show that 4 50s is "better" than 6 (just in terms of damage per second of fire), especially when you are comparing apples to apples (same MG type and caliber, and wing mountings).
I will give one caveat to the above, in some setups, I prefer the F4F-4 with 4 MGs, but only because of the increased ammo and firing time (usually in SEA setups).
That aside the Pony B is a fine ride, and I prefer it in some ways to the D, like others do, for the same reasons.