Your "AA weapons" are designed to KEEP bombers away from you, not to slaughter them. It certainly destroys them when they come close, as the bomber has made a mistake / took a risk in order to hit you easier with the supernova.
Flak and Solaris are not designed to hunt down bombers; they are designed to defend your ship against them. That's why they don't have longer range. If they did, a bomber would be forced to fight from the supernova's max range - good luck hitting with it. A single fighter / gunboat escort and primary turrets can easily deal with a bomber at over 1k distance.