I can, because the same rule applies, whether the books were written back in the 90's or not the same rule applies, having a good backstory in something that is not in the game itself should not be an excuse at all, from the perspective of a player that only played the Witcher 3 game, would he/she know of Eredin's character and plans and would he/she consider Eredin and interesting character like he was in the books? No, simple as that, which is disappointing seeing that I am an Eredin fanboyyou cannot compare Dragon age book with Witcher books... lol, books were written long before there was any plan for a PC game... W3 had to be true to the original book, they couldnt make Eredin something he was not... his intentions set in book were kept in all games - to wipe all elder blood humans, so there is no chance humans could get through the portal and attack them.
Yes, he had all the power and might he wanted, we hear of his intentions from Ciri and Avallac'h in the game, but that was not enough for his character development at all, he needed a lot more presence in the game, whether by having him send visions to Geralt to torment him or just adding more to his final scene in the game.not much to "flesh out... Eredin's intentions were set up in books quite well. He wanted to kill Ciri to prevent her offspring to destroy his world. He knew her child will be even more powerful than her, he didnt believed in Avalach's experiments, or attempts to force her to have a child with their former king. So, once he got rid of him he tried to kill her, and when she escaped, he just continued the chase. after all he was commander of Red Riders, he had all military power, nobody could challenge him..