There are theories that claim defending and counterattacking at the same time is superior due to it's speed advantages. But will it divide one's power and accuracy, causing a decrease in efficiency? Is it recommended to defend and counterattack seperately in a real life situation? And will that decrease the chances of being able to counterattack at all?
As a matter of fact, fighting does not work without defensive options. But at the same time, a sequential application of defensive and offensive moves does leave you with two options because your opponent typically does not stop with their attacks if not forced to do so:
- You are faster than your opponent, so much so that you can squeeze in an offensive move between two defenses
- You are more or less equally fast, so you end up defending and defending endlessly without ever getting an advantage
Since the latter does inevitably end up in an eventual mistake by you and thus being hit and even more of a tactical disadvantage, sequential application obviously is not an option. You could try to be the first to attack and keep them busy with defending all the time but truth be told, how realistic is that? Apart from being the first to go into the offensive obviously can cause legal problems in self-defense.
Therefore, you have no other option than doing both at the same time if you are to ever get out of the defense once an attack is coming at you.
This can take two forms:
You defend and attack in the same move, e.g. shifting sidewards and forwards and deflecting to avoid a cross and gripping/kneeing/hooking from your new, better position.
You use your defensive move in a way that offers you a strategic advantage, ie. you do not exactly attack at the same time but enable attacks, for example by pushing a low-kick-block out forwards and thereby breaking the opponent's balance. Or by evading a roundhouse and giving it a bit of extra-inertia with your hand to mess up your opponent's positioning and balance. Or by moving with a roundhouse or swinger to dampen the impact and blocking plus catching the limb for throws or joint manipulation. Endless options.
The way you posed your question seems to imply that the first option would basically overcharge us cognitively. That is not true. If you train both aspects as one move, your body learns the thing as one movement and acts accordingly, no matter whether you only move and deflect or move in and attack with the same move.
Therefore, just train to do both at the same time and that is exactly what you will be able to do when attacked for real.
Your question can evolve into a philosophical discussion very quickly, and each person's viewpoint will depend largely on what and how they were taught.
The point of view I am about to put forward is based on philosophies taught in karate, where it is expected that you will "win" the "fight" as soon as possible - this philosophy can still apply in part to ring combat but might be harder to execute due to rules and equipment.
I was taught very early on that there was no point defending, if you defend then you haven't progressed the fight at all. The opponent attacks, you defend, you're now both back to where you started - what is better is if your defense is actually an attack.
In a subsequent school I was taught there is no such thing as "defending". Our defensive moves - i.e. "blocks" or uke in karate parlance - were in fact attacks. Once I reached a belt level where bunkai was taught, I started to understand how a block was actually an attack. From that point on I never defended.
So going back to your question:
Is it efficient to defend and counterattack simultaneously?
I would answer that no, it is not efficient and there should only be counterattack, no defense.
Think of it this way: when an opponent throws a punch or a kick, they are extending an arm or leg towards you. My response will be to move and use a "block" against the incoming limb - i.e. like my description of the application of soto uke in this previous answer. When "blocking" most people initially think that you're only using the striking hand or forearm, but there's more than that - what do you think the other hand is doing? In most cases it is catching or parrying and it is an integral part of the "block". It could be argued that the parry/catch is a defense, but when executed with the rest of the move it is all attack, not defense. Your attack is the defense.