It is somewhat based upon the way BP explained that Shivan ships (their opponent) are set up - incredible advanced, but not directed. The fleet tries to adapt to this weakness - like the Iceni with its broadside cannons. Of course that bears the risk that the Shivans adapt, too...
Regarding diversity - imagine you have to fly an escort mission, you'll find yourself in front of several weapons that you can use...
-Short-range bomber suppression? Infyrno.
-Short-range fighter suppression? Piranha.
-Tactical bomber suppression? EMP Adv.
All of these weapons have a somewhat similar purpose, but even if you equip some of them to your wingmates, it's hard to use them really coherent.
I combined them to a weapon named Trianon - Explosive splitters (Infyrno), large central warhead that creates a shockwave (Piranha) and a EMP (EMP Adv.). While the Piranha (no homing submunition) and EMP (less range) loose some of their abilities, the resulting weapon is more powerful than any of the previous ones.
I viewed the dumpfire missiles as support for the primary cannons, that's why I thought the easiest why to develop them further is to combine them. I don't know how much space of the missile is filled out with the engine, but it seemed possible that by removing it you can probably double the amount of weapons you can take with you.
Californium is a real element, and there was a speculation whether Cf-251 could be used to built tiny nuclear weapons (but way too expensive), so I thought if GTVA can produce antimatter, they'd be able to do that too.