mod built in weapons are extremely powerful, i got a ship with a built in weapon called "Heavy Mjonir cannon" 1400 damage per shot.
They're also often unique to the ships that wield them, and that's part of what makes them so interesting. The Thermal Pulse Cannon is a bad example unfortunately because now EVERYONE has one in some form or other on their ships, but certain mod built-ins you really shouldn't see on other ships. After all, you want the
ship because of the
weapon it has, surely. That's what makes the ship cool. If you can just strip the ship of the weapon and use it elsewhere, why did the author bother making the weapon built-in in the first place?
Balance is another issue. It almost doesn't matter what kind of cost you put on such a mechanic, being able to put a normally built-in weapon on any old ship is objectively overpowered. Because you're exactly right! Built-in weapons ARE usually very powerful. They can afford to be because modularity (the ability to move weapons/fittings around on a ship) is actually a major strength. A weapon that is fixed to its carrier ship is stuck with that ship alone, so it can afford to be more powerful.
And if that doesn't convince you, being able to put a "built-in weapon" on any old ship has the potential to cause major errors within the game since a weapon may have scripted effects that tie in directly with the ship it's mounted on. I know of at least one ship with built-in weapons that have the ability to switch ammunition types based on the state of the ship's active system - even if putting those weapons on another ship doesn't cause a game crash because they can't find said ship system, those weapons won't work as well as you might think because they no longer have that system to control them.
