Idk know about that, they made it obvious to point out that she disappeared off screen and had not died visibly in the original novel. I think they are insinuating that she is doing more stuff behind the scenes and controlling people to the point that she can just disappear if she wanted. But this is just a guess
Actually, it was Leo’s point of view. Leo transmigrated from the modern world. Varia has always been part of this world. She just died and went back in time.
Leo was the one assuming Usis died.
I also said “if”. Meaning that there is the possibility Leo is wrong.
So IF, in the original work, she died from not being able to read the room, as Leo assumes, I stand by her character being rather useless.
Also, the reason why I said it's varia's pov is that the og!novel is in her narrative. So if she just disappeared from the novel, it's not really surprising cus she could just be unawarw of her capabilities. And leo sees the screen through varia's pov, making her bias assumptions.... Sorry if my explanation is a mess

Well if, in the original book, if she died painfullly because she couldn’t read the room, it sounds like Usis is useless.