A flak gun shot down fighters in the second world war, but not the fighers today !!
Now we use weapons like Hacksaw or chainsaw.
I think about a rebalance of the AA weapons.
--- Suggestion ---
Razor's Kiss: Faster box/unbox, 150 dmg/s, -15% range
Hacksaw: range +10%
Flak: each shot 315 dmg, 1 1/3 shots/sec, Air units can't be targeted, target ground units in 1/5 of range
Chainsaw: each shot 85 dmg, 4 shots/sec, -15% range
--- Effects ---
Flak works only against Gunships ( Not against gnat spam - you need defenders, llts or Razor's Kiss )
Hacksaw protect a larger area from Precision Bombers or Lichos ( if you build 2 or 3 of them )
Razor's Kiss is now a single point protection, but works great against air spam and can't get destroyed from air like till now.
Chainsaw - is now a very effective AA, but can't used anymore to shot down fighters over the enemys territory.