What you lose, though, at least in HG, is the battery benefit. 9 Triple Laser Turrets on 9 ships is not as powerful as 9 TLTs on a single ship, because the latter is considered a single battery and a single attack, whereas the former are separated within the system as 9 separate attacks.
Well depends on what you are playing. Remember High Guard is a fleet combat system, not a ship combat system.
But, I don't think that LBB2 has a similar combat effect. A Laser is a Laser in LBB2.
Your right, the individual laser is much more powerful in LBB2 than it is in HG.
So, as others have said, the advantages of fighters are simply the saturation of defenses in terms of "number of targets" limitations, and, perhaps, the higher ratio of weapons to tonnage. A 1000 ton ship can mount 30 lasers maximum. If you can deploy fighters to boost that maximum, then fighters will prevail.
You must remember ship's are limited to the number of different targets they can engage, or at least in LLB2.
I think your real answer is going to be in your frame of reference and rule set.
I run small ship games, with combat being some flavor of LBB2/Brilliant Lances, fighters are scary in numbers. If you are running a big ship game not so. All depends on what your doing.