I'm in my mobile and this could be really long, so I'll try to summarize it (all from a karate/taekwondo standpoint):
Originally there were no names for kata techniques, so what is a "block" could be very well a plain strike or whatever.
BUT in my opinion the most important point of this discussion is that there was never this simple "block" kind of technique. What karate (I can't speak for other arts but I believe the issue is similar) uses is UKE techniques, that comes from the verb ukeru and can be loosely translated as TO RECEIVE. It means that uke techniques are generally ways to respond against an incoming attack - many different ways to respond against many different kinds of attacks. And many times the response to the attack will include the counter (or lock/throw) as well, or some kind of unbalancing technique or a tactical repositioning of the defender's body. So it will never be a simple block.
The second big problem in my opinion is that most practitioners don't have a clue about the applications of uke techniques. So an uke waza ("receiving technique" ) can be very effective, but only if you know how to use it. Most people only focus on the last part of the technique as being the "block/deflection", while in my view most techniques do include some kind of blocking/deflection, but usually in the very beginning of the technique's motion (what would make the blocking faster as it comes from a single movement). Actually, many simple uke techniques begin with arms/hands crossed or both arms up in a way that resembles very well a "panic block", what uses to advantage a person's natural flinch reflex, and only the following movement is the really different part. Many of those "blocks" even do begin with a inward palm (or forearm) movement that is very similar to the typical boxing parry (think of most traditional blocking techniques). Obviously later (or simultaneously) you will counterattack, joint lock, throw or whatever (all within the same uke technique motion), but it will always be as a response from an attack and not an attack in and of itself - after all, karate was an art designated for CIVILIAN DEFENSE, not for civilian "offense".
Also we have to note that a good uke waza should always be performed with body movement as well (just like they are usually shown in kata), so yes, when you "block", you better "block" AND dodge - preferably at an angle.
Finally, over time in some styles the ways to perform some techniques have been diluted (for esthetics purposes or whatever) in such a fashion that it becomes much harder or impossible to relate them to the original intent meant for them.
So I believe all this "block" issue is a big misunderstanding because most uke waza are much more than mere "blocks", and the very translation - when correct - of "uke" shows this. But while the techniques had originally no names and certainly they have many applications (I myself teach many different applications for many uke techniques), I believe many or most of them have been generally adequately labeled as "uke", as they are indeed responses against attacks (many different attacks, including grabs, holds etc. - from different angles, including from behind - thus some crazy movements that don't seem to respond to anything in front of the defender's body). This said, I do believe that there can be a few techniques labeled as uke but being actually sole attacks - but I wouldn't be so sure.
There's one side note that some people think uke waza are not effective because they aren't used in MMA. I don't think so as I have seen many instances where the contestants have reacted to attacks in a way very similar to the correct (in my opinion) applications of uke waza, and achieving very good results. But however, the context of MMA is so different to the context of civilian defense that it would be ok if uke waza was useless in that case, because uke waza have not been created to be used in MMA. In CIVILIAN DEFENSE the opponents would hardly be circling around each other, trying to find or build openings in their defenses, making feints and controlling carefully the distancing. In a civilian defense context attacks are usually more careless (and even more telegraphed), and performed by untrained people and many times you won't even have a chance to preempt. If you are able to preempt, that is, use an attack instead of a response to an attack (an uke waza), that's great. But what if you aren't able to preempt? You'll obviously have to be trained in responding techniques too. Not mentioning the practical, moral and legal issues concerning preemptive attacks that make them a less likely option.
I tried to summarize my explanation, so please forgive me if something sounds not very consistent - maybe in that case I would have to explain further. We all know that when talking about those things we better not write - instead we should speak and show.
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