I’m surprised nobody’s mentioned this, but the guy in the other beatdown video was not doing aikido and was not an aikido master or anything remotely like it. He billed himself as a “aiki” master - ki is the same mystic energy that’s labeled “chi” or “qi” in Chinese, and “aiki” or “kiai” is the magical unification of your vital energy that’s supposed to be released by the shouting in karate etc.
His schtick, essentially the same as this Chinese tai chi master, was that his energy was so powerful that he didn’t need to know any technique. Whoops.
For all that aikido is oriented to peacefulness and non-lethal solutions, it’s still taught as a martial art, and in the dojos where I’ve studied there’s always been a healthy dose of “Now don’t do this technique hard and fast or you’ll probably dislocate their elbow or shoulder” and “If they don’t fall down when you do this, then that’s their own problem because then you’re perfectly positioned to punch them in the face hard with your other hand.” (This BTW is in the supposedly wimpier and more pacifist Ki-Aikido lineage of schools.)
Aikido does have some clear practical weaknesses. The biggest one, as with many other martial arts, is that beginners get a very simplified and idealized way of how an attacker will proceed, and can get an exaggerated idea of their own abilities due to working with an “attacker” who is cooperating to help them learn, and another of which is that its ideal is to keep your attacker at a distance, so it is weak in “mat” or grappling techniques. If you’re attacked suddenly by someone who’s already at close range when they start to attack, it’s certainly helpful to also know something like Wing Chun, or jiu-jitsu, or Muay Thai.* However its faults have nothing to do with that supposed “kiai” demo.
* or just basic boxing, of course.
Edit: reading more, I see one source says he claimed to be an “aiki” master as well as having psychic powers; earlier sources I’d read about him said he was claiming to be a master of “kiai”. Basically the same thing, and still not aikido, but I clarified my comment above.