Maybe 15 minutes gameplay isnt long enough to tell how a map is (and also im not a very experienced mapper), but I felt like the whole battle was taking place in the immedeat area of the control point. The attackers were constantly waiting around the two rocks on their side, and pushing through the building above, and it got very dull, perhaps it was my fault for constantly setting up sentries. Engineers are quite powerful (although there arent many positions to set a sentry up), I built a sentry that covered the whole middle section and could only be outranged by shooting from the upper building, got me a couple of kills.
What I like about Viaduct is that you have to decide whether to defend it from your side or push, standing on the point means you're an easy target since there are a lot of different angles from which the attackers can spam or snipe you. Engineers also can only build sentries which partially cover the point OR can be outranged.
I'd say add some new areas that can be held by the defending team on the attackers side, so you have an incentive to push further, and a third way to the CP (maybe alter the area that youme marked as useless and add it there?)