I quite like Ciri. And most people who I've seen and heard talk about the series like her as well.
Your opinion or your take on her that she's the worst character ever doesn't make it true.
It's just your opinion. One with which the vast majority of the witcher fanbase wouldn't agree with I'd wager.
To be fair, that was the purpose. They sanitizied her in the games. Probably to make her as likeable as possible for the players.
And it worked. I like her character more than in the books, but it also made her somehow more boring. She is too idealistic for my taste. Too perfect. The sexual aspect about her for instance. Pretty much almost everybody wanted to sleep with her or force her to sleep with somebody else was one of the main topics in the books and completely absent in the games. Or her time with the rats. When she did a lot of bad things . Killing innocents for pleasure should have a impact on her character. But we don't see any of it in the games. Her "worst" character trait is her obstinacy. I wished they would have touched others topics more.
Same applies to Geralt. It would have been interesting to lean more about his time as a Rider of the Wild Hunt. He probably killed innocents and kidnaped children. But we hear nothing about this in Witcher 3.
There is a interesting statement from Sapkowski
"Ciri personifies evil,that's how I intented her to be - a monster, because almost everyone is trying to make a monster out of her. Geralt, on the other hand, personifies good. And in that scene, a witcher and a girl are coming down a stairs, good and evil hand in hand - that's why no one can stop them. Does that mean that good dies at the end of the day? Yes. Does that mean that evil wins? No. Geralt dies and Ciri stops representing evil. Who is she, then? That, she doesn't know. And I won't tell you."