Yes that was what i am trying to express, concerning the witcher, because there are only a handful of "wizards" in the seting. Mostly the Ladies like Yennefer, Triss etc. and a handful of males also. At least if you are not counting in the elves from the other world, not the native ones. Clerics with powers like in D&D, there are none. Cannot even tell what religions are in the setting except the thing with the holy flame. All the mundane stuff does not need to be discussed, but something like a warlock would be considered a monster, which eventually needs to be hunted down by Geralt.
Edit: If i had to do such a conversion i would prolly use DSA rules they might fit perfectly its just refluffing, or eventually modified CoC rules but surely not D&D.