Another approach to making other launchers competetive with box launchers is to make it so no launchers actually store missiles anymore, and have box launchers load directly from magazine (but only can fire once before requiring an external reload).
The idea being that the magazine can be abstracted as also including the place where missiles are actually stored in the launcher
For clarity, how it currently works in VB6 aurora:
Normal Launchers -
(75% efficiency) Size 5 Magazine: 75 MSP
Size 5 Missile launcher at 5 HS, stores 5 MSP
Total HS: 10
Total Firepower: 1 per salvo
Total Sustained Firepower: 16, low cooldown.
Box Launchers -
Total Firepower: 14
Sustained Firepower: 14, instant.
How it works in the new system were all storage is now magazine only:
"No launcher storage" normal launchers -
(75% efficiency) 75 MSP magazine at 5 HS
Size 5 Missile launcher at 5 HS
total HS: 10
total firepower: 1 per salvo.
Sustained firepower: 15, low cooldown
Whereas the "no launcher storage" box launchers -
9 size 5 box launchers = 6.75 HS
45 MSP magazine is 3 HS
total HS: 9.75
total firepower: 9
sustained firepower: 9, instant.
This has several effects.
-General missile capacity is very marginally nerfed. Very slight, easily ignorable threshold.
-Magazine efficiency techs now effect box launchers, and as a result, box launchers become more size efficient the better your tech gets rather than stagnating as "exactly the same as it always is."
-Box launchers are nerfed, as are reduced launcher techs, in the sense that they simply no longer render full sized launchers almost obsolete by outclassing them in every meaningful way besides one (which it barely stands to match anyway). This is a slightly less applicable point, with the upcoming logistics update, but the fact that launchers carry vastly more power, flexibility, etc in roughly the same tonnage is a bit... overbearing.
-Armored magazines now have enough elbow room now to be considered potentially useful. You can even armor box launcher magazines to make the capacity line up the MSP with the amount of launchers you want on a particular vessel.
The exact direct mechanical change would be:
-Set the mag capacity of any launcher in of itself to 0.
-Everything would otherwise behave the same, though maybe make the ship maker pop an error if magazines have insufficient storage to fire a missile out of every single launcher once.