I'm not usually one of those people who needs things to be exactly like the books, but they did Vilgefortz so dirty in this. In the books, he's supposed to be the most powerful Mage of the time, and absolutely washed Geralt when they fought 1 on 1.
The fact that Cahir did that...big ole stretch.
I know I'm like a year late on these too, rewatching em in preparation for season 2 in December.