I think that's more due to Dorcas having a 20% Speed Growth whereas Hector has 35%. Dorcas may have 1 more point of CON but that's pretty useless without a decent speed stat to use it with.
Dorcas also has exactly the same base Strength and Strength growths as Hector (Base 7 with 60% Growth). I doubt the major difference in their utility is entirely down to Hector's better Defences and his Wolf Beil.
My point is that Hector is unique because his good CON allows him to use his high Attack/ Defence and his decent Speed to the maximum. It also allows him to wield heavy axes without taking a speed penalty, such as the Wolf Beil.
Likewise, during the late game, when Hector promotes to Great Lord and hits 15 CON, it means he can be using the Tomohawk and Armads without any speed penalty.
We might have to agree to disagree here though, since I found Hector double hit pretty often in my play throughs, particularly during the mid to late game.
If your experience is different then I can understand where you're coming from.