I use to hate it, but there are some guys that make great commentary on politics over videos not necessarily from YouTube. There are also a couple of channels that make very funny commentary on videos that I would never watch by myself.
I agree that not all reaction videos are bad. Sometimes the original video is just a video of the thing and as a lay person I need someone with more expertise to provide an analysis of the thing so I can understand it.
One example of the top of my head is "drummer reacts to Danny Carey" where he explains why the piece of music is so difficult but the original video is just Danny Carey performing the song. I dont know enough about drumming to understand the original video so it's nice to have someone break it down for me.
That would be commentary content, not reaction content. The key difference is that commentary content actually adds something of value or provides analysis, whereas reaction content does not
This is what separates channels like Knox Hill from all the basic music reactors