I honestly have no idea, but the military composite has been way easier to find (humvees, transports, etc.).
Also, I’ve always imagined superalloy as being heavier, though that is likely not the case.[/quote]
Its way weaker actually if i recall correctly.
I ll look it up sec 
edit:
mill composite : 3200 durabillity
superalloy : 900 dur
so it is actually a lot weaker.
your beter of installing hard plating or even steel armour xD
steel plating has 1000
and hard plating 2300
so i dunno … maybe its supossed to be weak or someone mixed up the values or something.