It should all come down to Fair Use. YouTube should, in a perfect world, have governance that equally punishes both uploaders who violate copyright and companies that file false DMCA claims.
A review, a DF technical analysis, or channels like Arlo and Jim Sterling that use footage in gaming discussions clearly fall under Fair Use. As do video game music covers.
Let's Plays? That's more of a grey area. If the LPer is providing some entertainment value or content beyond simply showing game footage, then it's probably Fair Use, but that's at the discretion of the copyright holder. So I have no problem at all with them using their discretion to shut down a particular LPer using their content to spread hate. They have the right to determine that it's not Faur Use, in this case.