I actually like AAA beams as a concept, ...
This post sums up my feelings nicely. AAA are frustrating to deal with, and that's pretty much their point. Retail FS2 is, ironically, firmly on lower end of AAA beam handling, as it often doesn't provide the player with proper tools to deal with them when they need to (although, as a general rule, retail gets a bit iffy when it comes to balance).
Was it necessary to make them this
powerful ? Not sure, I think they would have worked fine one of their 3 effects off to another turret type. Do I think they are overpowered ? Not sure either, however they are the only turret type you have to respect on every difficulty level.
RE : heavy fighters & difficulty levels
As you increase the difficulty level, a lot of thing changes in the tactical environment, strike crafts start filling much more specific niches.
Perseus basically becomes the go-to fighter as it's viable in pretty much every situation, even if it's not great at some of them. It's a good dogfighter that's small and fast enough to avoid taking full damage from flak guns.
Heavy fighter are great when defending or attacking warships, where they can use their increased loadout to lob tons of missiles at hostile warships and/or pelt them with sustained maxim fire, or use your thicker skin to aggro hostile fighters and draw them into friendly capship killzones. On the other hand, dogfighting the more agile fighters is going to be frustrating at best, and you get murderized by flak guns.
If you look at the other extreme, super agile fighters like the Serapis or Loki get extremely deadly in dogfight situation, whereas flying them just wasn't worth it in medium. On insane they're pretty much the only ones that stand a chance against Dragons.
Also, bombers are death traps. Fortunately, there's only 3 missions in which you have
to fly them - Slaying Ravana, The King's Gambit, and Bearbaiting (The Sicilian Defense allows you to fly a fighter).
Mister-eight-gun-boom-boom is still good, but you absolutely need to use the ETS to be really effective with it.