Motion and After Effects share some capabilities but they are not designed to compete. After Effects excels at complex compositing both in 2d and psuedo 3d. Motion's strength is motion graphics design and titling in ease of use. They are complementary programs. I used Motion on a recent projects to create simple animated backgrounds and titles, then used After Effects to composite video footage on top of these background. Both products technically could have done the whole project solely but I found the best approach is a little of both. Creating images is a little like cooking, there are many ways to arrive at a tasty meal.