For doing what exactly?
It's more about NOT doing than doing in the beginning.
Actually, throughout the books up until Witcher 3, Geralt's and Yen's efforts have been concentrated on teaching her how to survive and control her abilities. And teaching her lore and knowledge related to her abilities. And building her character to deal with her abilities and everything else that comes with it.
Only with Avallac'h do we realize he's been working on unlocking the full potential of the Elder Blood in order to stop the White Frost.
And still they made her self doubting and insecure...
Hence my comment, Alvin seems like a much stronger character and a better candidate for the job, considering his achievements with basically no information, training or support.
Within his own interpretation of reality, he's been and remained a hero.
I also feel compelled to comment in regards to folklore, all Witcher games and segments of books too, have Polish and Slavic folklore. I don't feel like CDPR owes anyone an explanation for these.
Witcher 1 has a whole chapter dedicated to one folklore tale, are you aware?
Just like English language uses idioms for everything, which make certain books and movies, maybe even games, very strange to non native speakers.