Fighters are extremely deadly, even more than MIRV Missiles.
Eh, I wish... fighters are a weird feature of MoO2. At the very start of the game they are ok or even good with Fusion Beams or Mass Drivers (granted, MIRV missiles will outclass them just a few turns later, but they still do their job). Then there's that very
long phase* (until Phasers or Particle Beams are available) in wich their damage stays the same, and everyone's defenses grow up, almost to the point of nullifying their effectiveness. Even if you have the patience to stick with fighters and get them Phasers technology, there's still the problem of them being too vulnerable against Pulsars and Lightning Fields. Heck, in a way they can even blow themselves up by killing something if you consider engine explosions.
Then add the fact that they cannot be controlled once launched, aren't really effective as missile defense, are very slow without a good engine technology...
*The thing with the damage is, Interceptors can only equip a modified version of your stronger point defense weapon, wich limits the options to literally 5 weapons: laser, fusion beam, mass driver, phaser, particle beam. The gap in damage and research time between Fusion Beam and Phasers is so huge it's baffling. There really should have been something in between, because as of now fighters risk to be useless for hundreds of turns.
And this is only made worse by shield mechanics, since fighers damage is calculated individually rather than for the whole squad. To make an example: if you have a squad of mass driver fighters (6 base damage, 4 ships) against a target with Shields III (-3 damage substracted to every hit), the formula used is (6 - 3) x 4 = 12. Very low damage, and greatly inefficent in terms of cost and space used.
Personally I love the idea of carriers and fighters, it reminds me of the good old times passed on Wing Commander, but the way they are implemented in MoO2, frankly, needs to be reworked.