You did notice you were talking of Demonstrations
and not Training
Further, I hate to break the news, but you can rarely prove or disprove the effectiveness of a technique by just practicing, even if you practice "free fighting". This way you could at most learn you don't know how to apply the technique in a situation
, which may stem from one of many reasons:
a. YOU have not practiced it enough
Just last week my Sensei asked us to practice Ikkyo against a Jab. Even in this specific and supposedly basic Waza, my partner kept failing while I had no problem at all and kept asking him to increase the pace, retract the Jab and launch a second etc. The reason was simple - he only practiced for a couple of years I have over a decade of practicing on him, and we used a practical variation of the technique which was beyond his abilities to control, so I had to help him make it work.
b. YOU miss identify the opportunity
This is one of my own major areas of development in the last couple of years, learning to correctly identify the opportunities for technique, and then apply the suitable technique. The difficulty is mostly in timing - the technique has to be there with the opportunity, if you have only saw the situation and then started thinking of the suitable technique, made up your mind and started moving, you will always be late and your technique will never work.
In my own mind, this is one of the more difficult part of Aiki to grasp, also known as softness and harmony -- utilizing any movement of an attacker for your technique set up. There are higher levels, such as channeling a non-cooperating attacker intent in your favor (much more difficult then the above which only requires you to "read his intent" and act on it).
c. Your teacher never taught you the technique in a practical way
A sad yet true fact for some, is that not all teachers understand \ care about practical techniques. Some teachers never learned how to practically utilize a technique themselves. I remember a Demo by a respected Aikido teacher, who tried to show Aikido is applicable to self defense, simply by increasing the speed in the demo, I was disappointed because Uke kept attacking in a telegraphed way, and gave up his own stability in advance, but the more disappointing thing was the teacher kept his techniques long and based on multiple-steps, and only increased his speed. The techniques were not instantaneous and the circles were huge (which practically left lots of room for Uke to regain his balance and counter).
Consistently practicing with "Free style play" can enhance your ability regarding the identification of opportunities (at least, this is our belief in Korindo Aikido and the one of the reasons we practice Kyoshu/Randori, see here for explanations - http://www.freewebz.com/aikido/lecture/unit6.htm)
. But, free play is always limited by your own model and safety, thus rendering it unreliable for any proof - I have seen people falling from bad techniques due to unjustified fear of a black belt (happened to me more then once).
There is a great difference between suffering some pain and taking damage, the latter does happen on occasion, but we keep trying to avoid it. Further, we try to use our Kyoshu/Randori as a learning tool for each student, and not as an examination laboratory. We do not test our techniques, we learn!
. Free play is a great time to teach one lots of things, from moving while being attacked (a most basic skill most people fail in during their first months. Often people fail even much later once placed under higher pressure then they are used to), through applying a technique in very slow yet non kata/waza settings, and up to reading and then leading\channeling intent. From our experience, we learn much more while practicing free play slowly (it is harder to practice in real slow motion, and not to jump your speed while you understand your mistake and see an hand going into your face).
One injury in five years is indicative of relatively safe martial practice. Though of course it depends how major the injury is. However, you should remember joint locks have the nasty tendency of causing more injury with much less power and speed compared to strikes\kicks. As the BJJ people like to say -- only light power is required once you have leverage. Striking arts enjoy a great practicing advantage in this respect -- you can apply much more power and speed and remain safe.
Further, the safety depends primarily on the control of Tori (the strike performer) and less on Uke (strike reciever) ability to withstand the strike. The same does not hold true for Aikido -- the safety relies primarily on Uke ability to evade the technique, Tori has to provide Uke with a safe solution. If Tori will press forward in full speed and strength and Uke will not have the time to respond, damage will occur (as has happened while practicing for the Kicking Demo I wrote about in my previous message) , Uke must not only know how to remain safe, but be able to utilize his safe conduit in the time Tori allocates him. Practicing in free style at full speed (for both sides) can hardly be done safely (as you can read in the link I provided -- it is possible but requires a great teacher to stop highly skilled practitioners in time and judge the result).
Lots of people often talk of practicing against resistance. Personally , I fail to see how one could really train Aikido style damaging locks against a resisting person without injury. How can you distinguish muscular and structural resistance? You should overcome the first, but if you crush trough the second you will create damage.
I do have some solutions we utilize, but they actually mean getting into the situation and stop there, before the lock is actually applied. Being Israeli and having learned with Israelis all my life, I always saw people trying to force their way out of a lock (and lots of people going home with very painful joints). As a supposedly advanced student, I have also shown people I can get into advantageous situation against their unschooled resistance while moving much slower then they (had they been schooled -- I would not have had a chance while moving slower). But I would be very careful about applying a technique in such situations, I may try, but trying is does not equate doing, I have caused enough damage acting the other way, as I progressed and learned.
Thus I can only repeat my previous response regarding the video -- It was a very nice demo of Aikido applied against kicking techniques
Oh, and I dislike the aikido Vs. ____ label it had. I saw a person demonstrating, not two M.A. fighting (ever seen a M.A. ???)