" Both Mitręga and Kalemba acknowledged a potential backlash from some corners of the internet at Ciri’s role as protagonist in The Witcher 4, but both insisted Ciri was always going to be the game’s main character."
Bullshit. Geralt was the series main character (he is THE literal Witcher). Ciri becoming a Witcher is simply what they try to fall back on to keep the series going, regardless of how unfaithful to the books it is.
I'd say if they weren't comfortable with a player-generated Witcher, Ciri does seem a natural choice.
Even though the main 5 novel series is called "Saga of the Witcher" Ciri becomes more and more significant from book to book.
Book 4, "Tower of the Swallow" basically belongs to her, she gets much more screentime and gets to do more significant shit than Geralt and his party of misfits. In book 5, "Lady of the Lake" they get a similar amount of space, but while Geralt mostly fucks around (literally) in Toussaint, until he receives a critical tip that allows him to move towards the 'endgame', Ciri travels between worlds, unveils many secrets of the multiverse (including the mystery of the Wild Hunt) and rapidly levels up for the final battle. During which they both get to kill an important baddie. Actually, Ciri kills her nemesis all by herself, while Geralt succeeds only with the help of Yennefer and Regis.
She's of course absent from CDPR Witcher 1 & 2 and only plays a supporting role in Witcher 3, but at the end of the second Expansion, it was evident that Geralt's only hoping for a retirement. I didn't want to play him in Witcher 4 and feel like the sentiment was shared by many fans. Forcing Geralt to go on another adventure once he managed to find solace in Corvo Bianco, preferably with his love interest, would be too cruel.
So it was either character creation, or Ciri. CDPR made their choice and I'm willing to let them cook and get a taste before passing judgement.