I don't think you're approaching Legolas' comment correctly. You've gone off on a giant rant about "game writing" vs "novel writing," primarily comparing the required skillsets. However, that's not really the issue at hand. Novelists didn't do the writing for The Witcher (PC game); game writers did. The game's story wasn't bad because they pulled in a novelist who knew nothing about the mechanics of writing games. The game's story was bad because the GAME WRITERS didn't do a good job.

To be honest, the only real issue I see up for debate, here, is whether it was their fault. Whether there is such a thing as a book inherently unsuitable for adaptation as a video game (keeping in mind that game writers have virtually unlimited flexibility to tweak things as necessary). I won't rule that out as a possibility, but I think it's highly unlikely.