[Bonus chapter thanks to TheAuthor137. I hope your family treated you like a plot hole this Christmas]
Intelligence wasn't just a matter of gathering a set of facts and acting on it. Maybe that would work on paper, but in the real world, people had varying emotional states, their own goals and aspirations, their own methods of doing things.
Sylas might seem like someone who did things strictly by the book, a man who lacked understanding of people. But he had never been like this.
As easily as he was able to decipher the words on a page, he could usually understand the inner workings of a person by observing them.
The reason Sylas was so intelligent was because he was capable of taking into account not only the facts on the ground but the hidden secrets in a person's heart.
