As much as Ethan Kline is a huge douche bag, he is large part of why you can use other people's videos in a transformative way under "fair use" on YouTube. He was sued in 2016 for making a reaction video, and he fought the lawsuit and won. Some info here: https://techraptor.net/technology/news/h3h3-productions-lawsuit-helps-start-fair-use-protection-account-fupa

I haven't seen a lot about the latest lawsuit, but my understanding is that he's claiming that streamers played his unedited content adding little to no transformative content or commentary over multiple hours which doesn't count as fair use.