But what are the opportunity costs of learning stuff on YouTube, especially if you're watching hours of content?
There is good stuff in there - don't get me wrong. It's just that the good stuff you want to find is often quite hidden, and I've on occasion spent more time trying to find some video that actually shows a tricky part of some bit of equipment maintenance than it would take to just do things the slow way (think "If you know the exact sequence of steps, you can slip the alternator out this hole between the engine and suspension - or you can just unbolt the exhaust and lower the alternator out that way" sort of tasks - if it takes longer to find a video with the steps clearly displayed than to just drop the exhaust, you've taken longer).
I've also found that YouTube leads to a very poor, surface understanding of most issues - and this isn't the fault of YouTube specifically, it's just a limit of video. If I want to learn about a new topic, I'll typically try to find three or so books on it and read those. A single book can have biases and misunderstandings, but by the time you've read a few, it's usually clear enough what the consensus is. Does it take more time than an hour or two video? Certainly. But I also get a far, far better understanding of the material (which, if it's an area I care to learn about, is probably useful) than I would through videos. Plus, I use an awful lot less data in the process.
I'm perfectly happy to be called a curmudgeon or such with regards to my preferences for text and images over video, and there may be part of it that's true - but I've weighed video versus the alternatives, and outside entertainment (which there's certainly some value in), I find video coming up wanting.
Also, books don't keep (buy this!) interrupting the content (buy that!) to feed me ads for (vote for this person because their opponent eats babies!) whatever happens to (watch this movie!) be paying the best rates (check out this new online bank and stock trading app!) at the moment.