You aren't looking at it right. It isn't the top tube in isolation. Its the ratio of head tube to top tube that I explained. If you compare the Defy, to both the Synapse and Roubaix there is close intersection. Comparing the top tube between race and endurance geometries is irrelevant. Most bikes in some size have every top tube length. Its the ratio that matters.
For example, a Roubaix at size 56 has both a taller head tube and shorter top tube than a Tarmac at size 58.

Hope this makes sense.