Plus, Sancto, the way the Swords are talked about and handled in the series it sets up their purpose and power to being "Very Special." There are ONLY three swords and they are forged by, and please please please remember I'm speaking in the idiom of the series, the nails of the Crucifixion. Which was, taken in the context of the culture, THE act of sacrifice that opened up heaven for all of humanity. That's some epic, once in a species ju-ju right there. So if weapons made of the nails of the White God's "only son"'s death, then that sets a benchmark. A high end mark. Can nothing surpass it? Well, no, of course not. But it'd have to be pretty damned impressive to pass it. Is Ferrovax the end all be all of creation? No, but you're hard pressed to find anything that rivals him. And denying "the Catch" to EVERYTHING is a fairly MASSIVE tactical advantage. Now, to be sure, one COULD read it that bypassing the Catch is the top tiered power that the greatest weapons the Powerful Beings give to mortal kind. Like...that's the greatest gift they can bestow, a way for humanity to level the playing field. So there IS that way to go. But even then, given what had to happen to get the relics to makes the swords, one would need something as epically scaled.
And to me, the "Swords of fallen angels," while the baddest assed metal album title I've heard in a while, doesn't sound like the same thing. It's so vague. And depending on who you listen to, those angels fight all the damned time, and there seems to be plenty of them, and they all have swords, and well...the swords are just our brain interpreting their "power" into a framework we get. Hardly seems the same scale of special as the nails of the cross. Maybe if the gun were made of something AS epic and came with the same rules and restrictions as the Swords it'd work. Because the Swords have uite the price. You do what God says. You follow His rules. One misuse could ruin everything.