Lasers and other beam weapons work by focusing a stream of light or particles on a spot for a while, but Starsector beams swing so wildly beams can focus only briefly
Even if the laser remains steady, the target ship would have to remain perfectly static relative to the laser weapon for it to be able to focus a spot to burn through thickness and layers of armor, which isn't a realistic option - unless you're a salvage ship hovering a wreck to cut apart lol. If the laser opens in bursts, each burst would only burn one layer in one specific spot each time.
Earlier in the thread I mentioned I was working on a total rework of weapons (including sprites, lore etc) using Realistic Combat as a base that I might post here. It's still WIP, but my current paradigms for beams are:
Lasers are fairly old weapons, and mostly effective at missile defense. Even heavier fighters shrug them off. If an older warship design has energy emplacements, it is typically only small turret mounts originally intended to carry lasers as PD.
Non-light particle beam weapons are more advanced, developed alongside more modern ships and power systems able to make them into practical combat weapons. Mainly intended to provide energy-focused ships with either long-range capability against armor (near instant kinetic beams, with heavy drawbacks) or long-range suppression capability using secondary effects. Some modern anti-fighter weapons are in this category as well.