Earlier quoted context omitted.
Once you understand the basics a high quality factory service manual is tough to beat. There’s plenty of low quality FSMs though, and most aftermarket repair manuals are awful. Videos can be helpful for learning fundamentals, but when I’m stuck on a specific problem not covered by the FSM, finding a hint or workaround happens fastest by searching forums rather than scrubbing through YouTube videos.
Not sure how to describe it but I cannot envision things at all while reading technical instructions. I own a few Haynes manuals and they do nothing for me no matter how many times I read them. I have a very visual memory. I managed to add a lift, change my CV shafts, lower control arms and a couple of other linkages by watching youtube. After doing it once, I can replay it from memory but that's not something a book…
To be fair, learning many mechanical tasks for the first time is really a combination of fundamentals and application specific details (this can apply to most fields outside your expertise). As you mentioned, you can repeat the same task again mostly from memory. You could then extrapolate that knowledge to a different vehicle by referencing the application specific details in a quality service manual.
Videos are helpful because you lack the fundamentals, and they can be great for that.