I wouldn't nerf flak guardians too hard though. They are beasty things, but they seem to die very easily ( I do like them, actually
).
At the minute they seem to be fulfilling the final knife in the back if you let them get in range. AOE overload is what's causing this I think; in some systems you might get ganged up on by lightning and flak guardians, meanwhile the artillery guardians are hitting you and the beam guardians are rolling into range.
It just kills fleets very fast unless you enter the system and immediately start kiting away as much of the damage as you can.
Edit: siege ships normally survive fairly well, the guardians seem to concentrate almost solely on the fleet ball.
PS: I hope to see the tractor beam guardians cropping up more to steal my ships