Gotta agree here, Ramsay pulled off some fantastic stunts and he's definitely bright. However, Roose is clearly a genius - he achieves his ends very subtley but achieves them well. He warns Ramsay several times about 'how his behavior will go over, can't he figure that much out?'
Ramsay is the kind of smart that lets him set a goal, and achieve that goal at the expense of the larger picture. The larger picture is simply too complicated for Ramsay to achieve without intervention. Some of his personal compulsions do get in his way, but do not appear to affect his ability to conceive complicated multi-pronged strategies.
Roose is the kind of smart that lets him set an overarching goal, and the pieces appear to fall into place by themselves through the actions of others. And he is still able to bail water for Ramsay and help Ramsay achieve his own goals, while still managing to pull together his larger picture.
There is a big difference between the level of intelligence with these two. One people can be impressed by, the other people can be both impressed and mystified by... The genius is the one who makes it seem easy and is able to help others while helping himself, able to allow others to do the work for him, while he gets the reward - and all of this on a grand "Game of Thrones" scale.