Several weapons from the library of esoteric artifacts can be found in flotsam boxes. The gravedigger has a use in digging up treasure even if broken. Repairing the others is near impossible: Broken weapons cannot be repaired with kits. Repairing them yourself would require the recipe, which is very hard to get on Siptah - and even if you have it, crafting new versions would be more efficient, as you’d get increased stats with a good blacksmith.
Is there a use for other broken weapons? Who knows.
Is this intended? Again, who knows.
I stashed them in case somebody finds a use someday. But currently, I’d say it’s okay to throw them away or shred them in the disassembly bench.