Those weapons are tools, designed to carve Nethicite, so it's to be expected that they won't be as powerful as weapons that are intended for combat and nothing else...

I found the Sword of Kings fairly useful the first time I got it, since it was relatively powerful compared to the rest of my arsenal at the time. However, I never use it in my newer games.

I don't recall exactly, but it stands to reason that both the Occurian swords will be gone from your inventory after the incident withe Sun-Cryst.