Just going to throw in my two cents here, skimmed over a lot of things that were brought up. Concerning Persona 5 and Atlus their case is much more understandable in my opinion, their game, while their gameplay is very copy and paste from their prior games, is a JRPG in the classic style and derives much of it's popularity in the series for it's Story. Atlus acting to keep players from streaming beyond a certain point is understandable for the preservation of their art and their ability to continue making that art. Is it against the law for them to do so, no. Is it against the law to enforce it, technically no, since they can claim to have the video taken down for using their Animated clips that have not been publicly released.
Personally speaking, when I am looking into buying a popular game, I look at several streamers and YouTubers, from TotalBiscuit, Super Best Friends, Angry Joe, Achievement Hunter and anyone else that may be taking part in the game to see if it's something that I would enjoy or have fun playing, looking primarily for solo play or trying in public lobbies. Most of these give me a very good idea as to if I would be interested in the game, and if I would enjoy it for a longer period of time.