What this shows is how anti-user closed app eco-systems are. Some users probably found his app very useful but can't use it because lawyers.
That's another trouble with so many of these mega companies now that don't seem to have any kind of instance of customer or end user support at all. It's easy to code auto response systems, and bots that track down spam and malicious software, but to get an actual person to review what is being done is nearly impossible.
Second, what's "actual content"? Official content only? Undoubtedly some people who searched for "top gear" were looking for exactly what this guy put out.
I agree that the approach is bonkers, but it's not an issue exclusive to "walled gardens".
I doubt you would use a DMCA takedown request for this. You'd just disable embedding of your videos in your youtube options. Youtube probably already knows when a video isn't requested from either youtube's website or the official youtube app.