Most traditionally taught blocks are exaggerated movements that are meant to be used as teaching tools.
Just like you start by punching from the hip chambered, so you could get a feeling for the mechanics involved mainly in the hip, but for some reason a great majority of Karate has become stuck on these ''school'' techniques and regard them as fully developed techniques.
The thing with blocks and reality is that the further a limb is from your body the weaker the force you can apply with it becomes which is why using your hands like anti missile batteries is a mechanically flawed thing to do, not to mention the other physics related factors involved.
Correct blocking is not a forceful action i.e chopping your forearm against a kick. A correct block is mostly done with your body and it's core you facilitate the movement according to whatever strike, kick, other technique you are blocking. Hands in blocking are above else meant to initiate a grappling technique or counterattack. The hands can be used to perform circular blocks or instead parry and counterattack.
At least that's my take on it :P