It's pretty cynical to call that knowledge useless. It's learning to do a thing you want to know how to do. That has use to you and often those around you. As for hard engineering problems, just because they're more complex doesn't make the knowledge less available. There's a massive amount of engineering knowledge free online, it only takes the initiative to go out and use it to learn it. The curriculum of many entire university degrees is now available for free online in a way its never been before.

I hear your skepticism and acknowledge it. But I think you're being a little too flip with your 99% figure as well as your definition of useless.

The point is not to take a hard engineering problem and turn it into a 5 minute solution. You're right. Not all problems can be reduced to short Youtube videos (although it is amazing how many can).

The point is to take what may have been considered a hard, even impossible, engineering problem and get it in the hands or head of someone who might someday come up with a new or better solution. Even if the ultimate solution takes years or decades, it's still a radical reduction in TTK.

Yes, finding something that teaches you how to do something you want to do is useless. Unless it's something YOU want to do, of course! Then it's fantastic.

Then replace a video with books. If I want to learn something hard, I can Google for the resources on the topic, quickly get the names of books considered the best resources humanity has on that subject, and then proceed to either Amazon or my favourite pirate source. All I can do in 10 minutes to half an hour, and then I can start learning. Contrast with the 80s, where you'd have to go to your local library, which may or may not have any book on the subject, and if it has, it's not necessarily the best.