The thing with lasers range vastly exceeding the firecontrol range cap, is that it causes an increase in damage done at the capped range, as well as throughout that range.
It needs to be noted though, that only the "Range Modifier" (given by Wavelength Tech) has any effect on the damage-dropoff, not the total range given.
A 120cm Laser and a 10cm Laser with the same Wavelength-Tech do exactly (excludung rounding of damage) the same percentage of their damage at the same range.
The actual damage is given by Damage*((Range-Modifier*10000km)/Distance-Of-Target) with a max of Damage, and a min of 1.
This is what makes Lasers (and similar working Beam-Weapons) pretty useless at high ranges even with good Firecontrols, since they do at most 1/5 of their damage at 600000km, and even less at higher ranges (or at lower Wavelength-Techs).
Since the minimum of the damage calculation is 1, the best Beam-Weapon for long-Range engagements (above a few 100k kilometers) is actually the Meson-Cannon, because it doesn't lose any of its damage due to range and is much much cheaper to produce than Lasers at high tech levels.
*Particle beams. But nobody loves particle beams, partially because of the hard cap on range. Mesons are generally only optimal for engaging targets on planets with atmosphere and heavily shielded ships, but the nice part about them is that their effectiveness can only be reduced by one thing: ships being so large that a single point of component damage is trivial (unless it pops a drive/magazine which then has its safeties fail).
The thing to keep in mind when comparing different beam weapons though, is the constrains under which they are to be used. Beam Ships generally have to be faster than their targets in order to actually reach them, which means that once they're in beam-engagement range, they can usually dictate the distance between them and their target. Since higher engagement ranges are usually preferable (especially due to missiles not being shot at by pointdefense if the distance is below the range the missile travels in 5 secs) and you're usually able to dictate the distance you fight at, the most practical comparison of beam weapons is their cost/size to damage-at-high-range-ratio.
And even with Shock-Damage, at high ranges the same HS of mesons (which are much cheaper) will outdamage High-Calibre Lasers or Particle Cannons, despite them being more than 10x as expensive per HS at high tech.
An example (600k engagement range):
60 cm Advanced Spinal Mount Laser(90cm total) with a Range Modifier of 8 and a Recharge of 12:
Size: 29HS
Cost: 1397
Damage(Max):212
Recharge time:90 seconds
Damage(Max) per second: 2,355
Damage(Max) per second per hs: 0,0812
Damage(range 600k) per second per hs: 0,0108
-with added Shock damage (which at most is 1/6 of the damage, but will probably be much less here, but 1/6 is assumed): 0,0126
25cm Meson with Focusing Tech of 8 and Recharge of 12:
Size:8HS
Cost:45
Damage:1
Recharge time:10 seconds
Damage per second: 0,1
Damage per second per hs: 0,0125
Damage(range 600k) per second per hs: 0,0125
So not only does the Meson do more damage per HS, it also costs 1/10 of the Laser AND ignores Shields and Armor.
edit: Ive just run the calculations for Particle Beams and they perform much better than I've expected, so they might actually be another valid choice for Beam Weapons, though Laser remain invalid imo (though Particle Beams still have the same issue of being expensive as fuck, which makes Mesons the most economically viable).