why else would they even try to engage a Demon-class destroyer with a cruiser as stated in the FS1 tech fluff?).
Hum... Because the fusion mortar was the most powerful weapon back in this era ? 
And why do no other cruisers aside from the
Fenris have the Fusion Mortar? Why do no destroyers have it, despite having massive amounts of space that are far in excess of what's needed to carry 150 fighters around? Where did FS1 ships (Typhon aside, but even that's borderline) find the energy to fire weapons hundreds of times as powerful as what they used to have? I prefer to think that the beam cannons on FS2 simply replaced existing heavy anti-cap weapons (whether they be INF:A style railguns, torpedo launchers like the Fusion Mortar, or other heavy weapons). The
Fenris is perhaps the only non-
Lucifer capship in FS1 that isn't ludicrously,
hilariously underarmed. These ships had the size and power to mount huge anti-cap weapons of some sort, it's insane to think that they could and did not.
Other things that corroborate my theory:
* The destruction of the GTD
Eisenhower and her escorts was attributed to the design of the PVD
Typhon herself, and not her fighter and bomber wings.
* The GTD
Bastion tried to chase the SD
Lucifer into the DS-Sol jump node. This indicates that the
Bastion intended to bring heavy weapons to bear on the
Lucifer while her shields were down; otherwise there would be no point.
Evidence suggests that the FS1-era Terran and Vasudan warships mounted considerable anti-capital weaponry and were powerful vessels in their own right, but less powerful than their FS2-era retrofit versions. Essential parts of the plot and backstory pretty much require this to be true.