They changed their strategic direction for the show.
Go back and re-watch the first season, then try to watch the next two.
The first season is trying to compete with what HBO used to be known for: high-budget spectacles. It's like a blockbuster movie stretched out into a series. The lighting, the costumes the editing, the special effects, the casting, the writing, the sound design. It's comparable to Game of Thrones, Stranger Things, Band of Brothers, Wanda Vision, The Last of Us, Breaking Bad, the Walking Dead, the Mandalorian, American Horror Story, Westworld, etc. Of course, those shows aren't all perfect but they have high production values (or at least started that way) and were meant to be premium technical showcases. Back before the days of streaming, this was the quality of show where you'd have to pay your cable company extra to get that channel.
Immediately with season 2 of the Witcher, everything feels worse. The most obvious to me is how Yennifer went from her ridiculous outfits to dresses that look like they're on sale at Kohl's today. The lighting, the makeup, everything. It's the quality of basic daytime cable TV, the kind that is still broadcast over the air for free.
Not surprising. The issues they had with Cavill were directly related to the fact that he knew the source material and how they were fucking it up.
Especially egregious since they were extremely vocal about staying true to the source material in the books, then immediately throwing that out the window after they got the names of places, characters, and general occupations.
First season was mostly fine, but those penis armored nilfgardians...
Second season completely undermined established characters' morals. Yen acting like a 60s "irrational female character" archetype because "I want a baby", Vesemir just being OK with the prospect of creating more witchers, the way they made Eskel out to be an asshole and then just killed him...
I don’t think the actor does, but the director and/or production has to. If it’s not similar to the source material just call it something else, but I do get saying “based on XYZ” makes for easier marketing.
Because he is not a fan of the series doesn't mean that he will do a bad job or skip on source material study. I guess I will reserve my judgment until I see a couple of episodes.
Because they didn't want a primary source. Especially not one that would try to correct them instead of letting them make their own shitty story in the universe and destroying existing characters in the process.