Tbf the success of the witcher was down to the way CDPR made it
Agreed, but you can't deny that the author made an excellent universe for some RPG action. CD Project are great storytellers, but their biggest games aren't using universes that they created.
He didn't deserve more money. But is what it is
That's debatable, and legally speaking, Polish Copyright law gave him the ability to have courts look at the old agreement. He was well within his rights to say the deal became unfair.
Was he a fool to create the old dead? Yes. Is he making more money from his books (and Netflix) because of CD Project's Success? Yes. Should he ask for more money from the videogames because he got an unfair deal? I don't know.
With article 44 of Poland's Copyright laws, he was legally allowed to have a court reexamine their contract. While it is true that CD Project Red created this "gross discrepancy" due to their own success, it is what it is.
"In the event of a gross discrepancy between the remuneration of the author and the benefits of the acquirer of author's economic rights or the licensee, the author may request that the court should duly increase his remuneration."
Ultimately, both sides have agreed and CD Project seems to have more freedom while Sapkowski has a better deal. Everybody wins.
I just think that people are underselling how much the creation of a solid universe impacts a big RPG like The Witcher. There's a reason why Cyberpunk is based on an existing IP with a lot of pre-done worldbuilding.