the B-29 in AH, I'm not thinking that a vast majority of intercepting aircraft will be of Japanesse nationality but rather of all varieties, thus we can speculate in this situation had historical B-29 crews had to of faced tougher attacking aircraft and had the choice of removing or keeping the 20mm they would of likely opted to keep the 20mm
Neither were they flying at full-frakking-throttle (the term FFT as it applies to AH refers mostly to bombers), nor were they taking off for 1000-mi missions with 25% fuel in the tanks, nor were they climbing at 2000fpm because they took less fuel, nor did they have no fear about the engines melting shortly after takeoff.....
In the real world, this plane was far less powerful than it will be as-modeled in AH. This is not to say I KNOW how HTC has modeled it, but they will follow the pattern set forth by all other bombers currently in this game (B-17, B-24, Lanc, etc).