flak- very good.
One thing I'd like to point out is the attack types. I'm unsure if anyone else has pointed this out (too lazy to read 8 pages), but capital ships all use the same attack type.
All attack types have a CHANCE TO HIT against SC. Which means- there's a chance that it won't even HIT the enemy SC. In the case of Capitals, it has a 10% chance to hit bombers or interceptors (fighters). Which means- 90% of the shots fired by a capital ship's weapons WILL NOT EVEN HIT THEIR TARGETS. Thus, caps can shoot back, but rather ineffectively, against SC.
Of note is that all the races' fighter SC have VeryLight armor, while all races' bomber SC have Light armor. The damage % multipliers against these armor types for the CAPITALSHIP attack type are as follows (taken from the Gameplay.Constants file, Entrenchment 1.03 version): CAPITALSHIP dmg type vs. VeryLight armor type- 25% damage multiplier (does 25% of the weapon's damage to the armor type), while against Light armor it does 75% of it's normal damage against the armor type.
Ergo, capital ship flak would only be effective against bombers, not fighters. Bombers have Light armor because Fighters use an ANTILIGHT attack; Fighters use 'VeryLight' armor and Flak Frigs have the ANTIVERYLIGHT attack. Attack types and armor types are actually what helps determine what units shoot at what other units. The damage % multipliers also do the same thing, but further differentiate the unit strengths.
Ultimately, capital ship flak is something easily feasible, and against swarms of fighters, would be only midly effective, while it would be more effective against bomber swarms.
A level 1 Kol Battleship has an autocannon damage of ~30-40 DPS. We'll call it 40 for right now. Now, against fighters, it would therefore only do 10 DPS, due to the 25% multiplier, while against bombers it would do 30 DPS.
I chose 40 DPS as the base for the above example because it is simpler to multiply it out. Overall, the easy thing to do would be SLIGHTLY (like 5% at most) buff bombers' health, to improve survivability. Even then that might not be needed.