Drop bear, great video to work with for discussion:
I think we could discect this and learn a few things, maybe clear a few things up. Lots of branches to this, including the fact that the video demonstrates the realistic grappling ability cadets get to in a typical academy setting. It's not a high degree of skill at all. I know because I taught them. You just don't get very many training hours with a cadet. Most of them start with zero experience fighting or wrestling.
Watching the video it was clear before hands were put on the suspect that the straight arm bar wasn't going to work. Any experienced grappler could see that, of course cadets generally aren't experienced grapplers. So it was attempted anyways.
The straight armbar works best when the officer archives the "escort position" prior to resistance. This didn't happen in the video. So it was a bad technique to try in this case. This is why all conflict is problem solving. The armbar is not THE SOLUTION, far from it!!! Like everything it is A WAY of putting someone into cuffs that doesn't comply verbally.
Other options include the grappling techniques you have suggested. Those certainly have their place, and would have been AN OPTION in this case, but not THE WAY to do it. The officer might have chose to use tools like the TASER or spray, if they weren't confident in essentially wrestling with a suspect. Either because of the officers low skill level at wrestling, or maybe the fact they were alone and didn't have a partner.
Wrestling with a suspect with a gun on your hip, is a highly dangerous activity. I have done it multiple, multiple times. It takes a very different mindset, focus, awareness and skill than you use in the gym. It is not something to be entered into lightly as an inexperienced officer or novice grappler. When you have more officers present, you can take higher risks by wrestling. Because if you begin to be dominated by a better wrestler, you have some or multiple people to help you.
But casually going for a takedown and closing with a suspect is highly dangerous, and the techniques presented by Iron Mike work(I have used them) but they are not the missing link to keeping suspects and officers safe. In fact it could easily create a situation where the suspect is shot and killed, when he otherwise would not have been.