But it has regardless been criticised. Why not employ a tight boxing guard? It's no fun kicking an elbow. When you do a downward block it doesn't actually hurt much to kick the blocking wrist, but it does against elbows.
Why confuse guard with blocking techniques?
Knockdown karate use a close distance and use a boxing-like guard (slightly lower hands in order to protect the ribs with the elbows since you only have to worry about kicks/knees to the head, not punches). Taking kicks on the elbow is basics.
Point karate (often wrongly called traditional karate) use very long distances, and has the guard much further out, in order to deflect incoming attacks before they get close.
Classic karate does not really bother about guard, as it is about self defense. And in self defense, you do not square up with a opponent for a exchange of tactical give and take while circling each other with refined footwork. You get in, get out, get away.
Noone who knows what they are doing (sadly, many karate practitioner does not) do hard downward blocks. you use it to deflect an incoming attack, not stop it cold.'
Ofcourse you could also do a lot of other stuff with it under the old karate adage that "a punch is not always a punch, a kick is not always a kick, and a block is hardly ever a block" but that is another matter.
https://www.youtube.com/watch?v=ylULQU-ouhU