Hmmm ... I've straight armbarred a ****load of guys without "rotating" the arm. You need to control the wrist, usually via the thumb, so they cannot spin out, and there are different philosophies about the final position of the wrist, but I've never had major problems just isolating the end of the lever (wrist), pinning it to my chest and extending the arm using my posterior chain. I've yet to meet someone who could come close to resisting this using arm strength once you control both ends of the lever. His bicep vs your posterior chain. No contest.
Armbars do have a fair number of details and a few differences of opinion about how to apply them, like most things.
Rotation can be useful in setting up the armlock, per Rhonda Rousey, but I've never been taught this rotation thing. I've been taught armbars by three of the Machado brothers, John Will, Richard Norton, Anthony Perosh and Gui Mendes.
Perhaps you are talking about a cutting armbar? For those I would agree the position of the elbow per rotation is very important.
It would be difficult to learn either of these via video alone. But once you understand the basic technical idea and principles behind it, I think the tweaks can be communicated on video and fine tuned by feel without difficulty.
Sorry I was referring to an armbar takedown from a standing position, not an armbar in terms of getting a submission or on the ground etc. If that helps to clarify things. Now some as I understand it may refer to this more as an "armlock" vs "armbar". I was always taught to call it an armbar. /shrug.
This is not a bad video, but not great either. I would place it in the "meh" category...
If they are strong/drunk/high enough it is possible for them to muscle out of such if you are just dropping your body weight down. However, if you start more with your wrist in the area of the tricep as the video says, rolling or driving your arm into/across, rotating his arm under yours as you drop, it messes with his shoulder in multiple directions. As my Guro says "the human brain likes linerar and hates circles" and adding this dynamic makes it much easier to take down.
The problem is, without an instructor, and a willing partner, it is dang hard to learn. First you have to look really close in the video though to see how the white t-shirt guy's arm is rotating at the shoulder to start with. Second, being sure that is happening in training can be difficult, because obviously you don't want to go so hard as to cause injury. Also this video in particular is speaking purely from a LEO/security perspective starting with the escort position and isn't showing how to properly transition during an on going "striking" fight.
In comparison we have this video
which is relying almost entirely on your body weight. It is an easy to learn technique but more than once, in reality, I have seen this fail due to size difference/intoxication.
Now do grappling specific arts have different techniques? Yes, I was thinking through my Kali lens as it applies to street encounters however and this is where I see an issue.
If you want to learn a particular art I wouldn't suggest any "free" videos on YouTube. There are some that I think are good for the following purpose I think they can be good. Once you have a solid base videos can help show you what does and what doesn't work outside the school and on the street, as an example. What I have a problem with videos, especially the "free ones" you find is the following.
1. There is really no vetting beyond "likes" and that to me is unreliable.
2. The ones from quality instructors are usually purposefully limited as they are really there as advertisement not bonafide instruction.
3. The most important one. On our best day, as humans, we can often find it difficult acknowledging mistakes when we are in a position to clearly see and thus critique our own actions. Now magnify that dynamic due to the fact that we can not see ourselves in the third person. Magnify it further because we may be trying to assimilate something that really requires a partner who is not there. Magnify it still further because, as a student, we don't even really know what to look for in terms of errors.