Good players will be able to glean information from a video, without being distracted by the fight itself. People CAN learn things from videos.
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People have different learning styles. Watching a video may work for some, while hands on doing things is better for others. Please consult the following video to learn more about different learning styles before having a discussion about the topic:
https://www.youtube.com/watch?v=-Jwz_h0zXsY
I don't see how Mr. Happy's videos are worthless. Even if you don't find the commentary particularly useful, you're seeing the fight play out. It's considerably more experience than you'll bring into the fight having not seen ANYTHING of it beforehand. He attempts to make them more useful to new players by adding the commentary to explain things, but you don't even need that if you're just trying to figure out mechanics ahead of time by watching.
It's not for everyone, but it's something.
The whole game is about phases/rotation. Knowing the order of kill, the positioning, what ability to use, etc is all extremely helpful. Will you be able to one shot it or kill it quick if you watch a video? Nope. Does it speed up the learning process? Yup. Can players still suck after watching a video? Yup.