not to put words in dan's mouth, but i think i can answer one of your questions.
you said: "Already you are showing a major strategic difference between boxing and karate. The follow-through makes the rapid snap-back needed for the SPEED of the techniques that will follow. So your ascertion that the snap back does not help speed, seems to be only taking into account the single punch, not the combination that the jab is setting up."
quick reteactions will let you throw punches in faster combinations, and if you want to spend time toe to toe unloading on your target, then thats the way for you hands down. if your using your karate studies for self defence then punching can take on a different role in the fight. the punch can strike on "a funny angle" to off ballance, then it grabs and pushes or pulls into a throw, sweep or trip. so instead of a 3 punch combination, you can use a punch, shove, trip.
so, its about different strategy. you can't use it in a boxing ring because of the rules, but outside no one has a pentent on it. tersm like effecient and effective are situational, like every freaking thing....
its not supposed to make sense